shared: Introduce new top-level dir and move 1st party lib code there.

This commit moves all first-party code developed for this project from lib/
to shared/, so that lib/ now only contains third-party code.

The following directories are moved as-is from lib to shared:

    lib/libc            -> shared/libc
    lib/memzip          -> shared/memzip
    lib/netutils        -> shared/netutils
    lib/timeutils       -> shared/timeutils
    lib/upytesthelper   -> shared/upytesthelper

All files in lib/embed/ have been moved to shared/libc/.

lib/mp-readline has been moved to shared/readline.

lib/utils has been moved to shared/runtime, with the exception of
lib/utils/printf.c which has been moved to shared/libc/printf.c.

Signed-off-by: Damien George <damien@micropython.org>

36 files changed, 4363 insertions, 0 deletions

diff --git a/shared/libc/__errno.c b/shared/libc/__errno.c
new file mode 100644
index 000000000..86417a02d
--- /dev/null
+++ b/shared/libc/__errno.c
@@ -0,0 +1,13 @@
+// This file provides a version of __errno() for embedded systems that do not have one.
+// This function is needed for expressions of the form: &errno
+
+static int embed_errno;
+
+#if defined(__linux__)
+int *__errno_location(void)
+#else
+int *__errno(void)
+#endif
+{
+    return &embed_errno;
+}
diff --git a/shared/libc/abort_.c b/shared/libc/abort_.c
new file mode 100644
index 000000000..3051eae81
--- /dev/null
+++ b/shared/libc/abort_.c
@@ -0,0 +1,7 @@
+#include <py/runtime.h>
+
+NORETURN void abort_(void);
+
+NORETURN void abort_(void) {
+    mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT("abort() called"));
+}
diff --git a/shared/libc/printf.c b/shared/libc/printf.c
new file mode 100644
index 000000000..e8db2b999
--- /dev/null
+++ b/shared/libc/printf.c
@@ -0,0 +1,133 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/mpconfig.h"
+
+#include <stdint.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include "py/obj.h"
+#include "py/mphal.h"
+
+#if MICROPY_PY_BUILTINS_FLOAT
+#include "py/formatfloat.h"
+#endif
+
+#if MICROPY_DEBUG_PRINTERS
+int DEBUG_printf(const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = mp_vprintf(MICROPY_DEBUG_PRINTER, fmt, ap);
+    va_end(ap);
+    return ret;
+}
+#endif
+
+#if MICROPY_USE_INTERNAL_PRINTF
+
+#undef putchar  // Some stdlibs have a #define for putchar
+int printf(const char *fmt, ...);
+int vprintf(const char *fmt, va_list ap);
+int putchar(int c);
+int puts(const char *s);
+int vsnprintf(char *str, size_t size, const char *fmt, va_list ap);
+int snprintf(char *str, size_t size, const char *fmt, ...);
+
+int printf(const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = mp_vprintf(&mp_plat_print, fmt, ap);
+    va_end(ap);
+    return ret;
+}
+
+int vprintf(const char *fmt, va_list ap) {
+    return mp_vprintf(&mp_plat_print, fmt, ap);
+}
+
+// need this because gcc optimises printf("%c", c) -> putchar(c), and printf("a") -> putchar('a')
+int putchar(int c) {
+    char chr = c;
+    mp_hal_stdout_tx_strn_cooked(&chr, 1);
+    return chr;
+}
+
+// need this because gcc optimises printf("string\n") -> puts("string")
+int puts(const char *s) {
+    mp_hal_stdout_tx_strn_cooked(s, strlen(s));
+    char chr = '\n';
+    mp_hal_stdout_tx_strn_cooked(&chr, 1);
+    return 1;
+}
+
+typedef struct _strn_print_env_t {
+    char *cur;
+    size_t remain;
+} strn_print_env_t;
+
+STATIC void strn_print_strn(void *data, const char *str, size_t len) {
+    strn_print_env_t *strn_print_env = data;
+    if (len > strn_print_env->remain) {
+        len = strn_print_env->remain;
+    }
+    memcpy(strn_print_env->cur, str, len);
+    strn_print_env->cur += len;
+    strn_print_env->remain -= len;
+}
+
+#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 9
+// uClibc requires this alias to be defined, or there may be link errors
+// when linkings against it statically.
+// GCC 9 gives a warning about missing attributes so it's excluded until
+// uClibc+GCC9 support is needed.
+int __GI_vsnprintf(char *str, size_t size, const char *fmt, va_list ap) __attribute__((weak, alias("vsnprintf")));
+#endif
+
+int vsnprintf(char *str, size_t size, const char *fmt, va_list ap) {
+    strn_print_env_t strn_print_env = {str, size};
+    mp_print_t print = {&strn_print_env, strn_print_strn};
+    int len = mp_vprintf(&print, fmt, ap);
+    // add terminating null byte
+    if (size > 0) {
+        if (strn_print_env.remain == 0) {
+            strn_print_env.cur[-1] = 0;
+        } else {
+            strn_print_env.cur[0] = 0;
+        }
+    }
+    return len;
+}
+
+int snprintf(char *str, size_t size, const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = vsnprintf(str, size, fmt, ap);
+    va_end(ap);
+    return ret;
+}
+
+#endif // MICROPY_USE_INTERNAL_PRINTF
diff --git a/shared/libc/string0.c b/shared/libc/string0.c
new file mode 100644
index 000000000..19ad14d0f
--- /dev/null
+++ b/shared/libc/string0.c
@@ -0,0 +1,254 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#define likely(x) __builtin_expect((x), 1)
+
+void *memcpy(void *dst, const void *src, size_t n) {
+    if (likely(!(((uintptr_t)dst) & 3) && !(((uintptr_t)src) & 3))) {
+        // pointers aligned
+        uint32_t *d = dst;
+        const uint32_t *s = src;
+
+        // copy words first
+        for (size_t i = (n >> 2); i; i--) {
+            *d++ = *s++;
+        }
+
+        if (n & 2) {
+            // copy half-word
+            *(uint16_t*)d = *(const uint16_t*)s;
+            d = (uint32_t*)((uint16_t*)d + 1);
+            s = (const uint32_t*)((const uint16_t*)s + 1);
+        }
+
+        if (n & 1) {
+            // copy byte
+            *((uint8_t*)d) = *((const uint8_t*)s);
+        }
+    } else {
+        // unaligned access, copy bytes
+        uint8_t *d = dst;
+        const uint8_t *s = src;
+
+        for (; n; n--) {
+            *d++ = *s++;
+        }
+    }
+
+    return dst;
+}
+
+void *memmove(void *dest, const void *src, size_t n) {
+    if (src < dest && (uint8_t*)dest < (const uint8_t*)src + n) {
+        // need to copy backwards
+        uint8_t *d = (uint8_t*)dest + n - 1;
+        const uint8_t *s = (const uint8_t*)src + n - 1;
+        for (; n > 0; n--) {
+            *d-- = *s--;
+        }
+        return dest;
+    } else {
+        // can use normal memcpy
+        return memcpy(dest, src, n);
+    }
+}
+
+void *memset(void *s, int c, size_t n) {
+    if (c == 0 && ((uintptr_t)s & 3) == 0) {
+        // aligned store of 0
+        uint32_t *s32 = s;
+        for (size_t i = n >> 2; i > 0; i--) {
+            *s32++ = 0;
+        }
+        if (n & 2) {
+            *((uint16_t*)s32) = 0;
+            s32 = (uint32_t*)((uint16_t*)s32 + 1);
+        }
+        if (n & 1) {
+            *((uint8_t*)s32) = 0;
+        }
+    } else {
+        uint8_t *s2 = s;
+        for (; n > 0; n--) {
+            *s2++ = c;
+        }
+    }
+    return s;
+}
+
+int memcmp(const void *s1, const void *s2, size_t n) {
+    const uint8_t *s1_8 = s1;
+    const uint8_t *s2_8 = s2;
+    while (n--) {
+        char c1 = *s1_8++;
+        char c2 = *s2_8++;
+        if (c1 < c2) return -1;
+        else if (c1 > c2) return 1;
+    }
+    return 0;
+}
+
+void *memchr(const void *s, int c, size_t n) {
+    if (n != 0) {
+        const unsigned char *p = s;
+
+        do {
+            if (*p++ == c)
+                return ((void *)(p - 1));
+        } while (--n != 0);
+    }
+    return 0;
+}
+
+size_t strlen(const char *str) {
+    int len = 0;
+    for (const char *s = str; *s; s++) {
+        len += 1;
+    }
+    return len;
+}
+
+int strcmp(const char *s1, const char *s2) {
+    while (*s1 && *s2) {
+        char c1 = *s1++; // XXX UTF8 get char, next char
+        char c2 = *s2++; // XXX UTF8 get char, next char
+        if (c1 < c2) return -1;
+        else if (c1 > c2) return 1;
+    }
+    if (*s2) return -1;
+    else if (*s1) return 1;
+    else return 0;
+}
+
+int strncmp(const char *s1, const char *s2, size_t n) {
+    while (*s1 && *s2 && n > 0) {
+        char c1 = *s1++; // XXX UTF8 get char, next char
+        char c2 = *s2++; // XXX UTF8 get char, next char
+        n--;
+        if (c1 < c2) return -1;
+        else if (c1 > c2) return 1;
+    }
+    if (n == 0) return 0;
+    else if (*s2) return -1;
+    else if (*s1) return 1;
+    else return 0;
+}
+
+char *strcpy(char *dest, const char *src) {
+    char *d = dest;
+    while (*src) {
+        *d++ = *src++;
+    }
+    *d = '\0';
+    return dest;
+}
+
+// Public Domain implementation of strncpy from:
+// http://en.wikibooks.org/wiki/C_Programming/Strings#The_strncpy_function
+char *strncpy(char *s1, const char *s2, size_t n) {
+     char *dst = s1;
+     const char *src = s2;
+     /* Copy bytes, one at a time.  */
+     while (n > 0) {
+         n--;
+         if ((*dst++ = *src++) == '\0') {
+             /* If we get here, we found a null character at the end
+                of s2, so use memset to put null bytes at the end of
+                s1.  */
+             memset(dst, '\0', n);
+             break;
+         }
+     }
+     return s1;
+ }
+
+// needed because gcc optimises strcpy + strcat to this
+char *stpcpy(char *dest, const char *src) {
+    while (*src) {
+        *dest++ = *src++;
+    }
+    *dest = '\0';
+    return dest;
+}
+
+char *strcat(char *dest, const char *src) {
+    char *d = dest;
+    while (*d) {
+        d++;
+    }
+    while (*src) {
+        *d++ = *src++;
+    }
+    *d = '\0';
+    return dest;
+}
+
+// Public Domain implementation of strchr from:
+// http://en.wikibooks.org/wiki/C_Programming/Strings#The_strchr_function
+char *strchr(const char *s, int c)
+{
+    /* Scan s for the character.  When this loop is finished,
+       s will either point to the end of the string or the
+       character we were looking for.  */
+    while (*s != '\0' && *s != (char)c)
+        s++;
+    return ((*s == c) ? (char *) s : 0);
+}
+
+
+// Public Domain implementation of strstr from:
+// http://en.wikibooks.org/wiki/C_Programming/Strings#The_strstr_function
+char *strstr(const char *haystack, const char *needle)
+{
+    size_t needlelen;
+    /* Check for the null needle case.  */
+    if (*needle == '\0')
+        return (char *) haystack;
+    needlelen = strlen(needle);
+    for (; (haystack = strchr(haystack, *needle)) != 0; haystack++)
+        if (strncmp(haystack, needle, needlelen) == 0)
+            return (char *) haystack;
+    return 0;
+}
+
+size_t strspn(const char *s, const char *accept) {
+    const char *ss = s;
+    while (*s && strchr(accept, *s) != NULL) {
+        ++s;
+    }
+    return s - ss;
+}
+
+size_t strcspn(const char *s, const char *reject) {
+    const char *ss = s;
+    while (*s && strchr(reject, *s) == NULL) {
+        ++s;
+    }
+    return s - ss;
+}
diff --git a/shared/memzip/README.md b/shared/memzip/README.md
new file mode 100644
index 000000000..287d0fc48
--- /dev/null
+++ b/shared/memzip/README.md
@@ -0,0 +1,28 @@
+MEMZIP - a simple readonly file system
+
+memzip takes a zip file which is comprised of uncompressed files and
+and presents it as a filesystem, allowing Python files to be imported.
+
+The script make-memzip.py takes a directory name and will create a zip file
+containing uncompressed files found in the directory. It will then generate
+a C file which contains the data from the zip file.
+
+A typical addition to a makefile would look like:
+```
+SRC_C += \
+    lib/memzip/import.c \
+    lib/memzip/lexermemzip.c \
+    lib/memzip/memzip.c \
+
+OBJ += $(BUILD)/memzip-files.o
+
+MAKE_MEMZIP = ../lib/memzip/make-memzip.py
+
+$(BUILD)/memzip-files.o: $(BUILD)/memzip-files.c
+    $(call compile_c)
+
+$(BUILD)/memzip-files.c: $(shell find ${MEMZIP_DIR} -type f)
+    @$(ECHO) "Creating $@"
+    $(Q)$(PYTHON) $(MAKE_MEMZIP) --zip-file $(BUILD)/memzip-files.zip --c-file $@ $(MEMZIP_DIR)
+```
+
diff --git a/shared/memzip/import.c b/shared/memzip/import.c
new file mode 100644
index 000000000..2d5225b88
--- /dev/null
+++ b/shared/memzip/import.c
@@ -0,0 +1,17 @@
+#include <stdio.h>
+
+#include "py/lexer.h"
+#include "memzip.h"
+
+mp_import_stat_t mp_import_stat(const char *path) {
+    MEMZIP_FILE_INFO info;
+
+    if (memzip_stat(path, &info) != MZ_OK) {
+        return MP_IMPORT_STAT_NO_EXIST;
+    }
+
+    if (info.is_dir) {
+        return MP_IMPORT_STAT_DIR;
+    }
+    return MP_IMPORT_STAT_FILE;
+}
diff --git a/shared/memzip/lexermemzip.c b/shared/memzip/lexermemzip.c
new file mode 100644
index 000000000..6b26961bd
--- /dev/null
+++ b/shared/memzip/lexermemzip.c
@@ -0,0 +1,19 @@
+#include <stdlib.h>
+
+#include "py/lexer.h"
+#include "py/runtime.h"
+#include "py/mperrno.h"
+#include "memzip.h"
+
+mp_lexer_t *mp_lexer_new_from_file(const char *filename)
+{
+    void *data;
+    size_t len;
+
+    if (memzip_locate(filename, &data, &len) != MZ_OK) {
+        mp_raise_OSError(MP_ENOENT);
+    }
+
+    return mp_lexer_new_from_str_len(qstr_from_str(filename), (const char *)data, (mp_uint_t)len, 0);
+}
+
diff --git a/shared/memzip/make-memzip.py b/shared/memzip/make-memzip.py
new file mode 100755
index 000000000..9730f5e00
--- /dev/null
+++ b/shared/memzip/make-memzip.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python
+#
+# Takes a directory of files and zips them up (as uncompressed files).
+# This then gets converted into a C data structure which can be read
+# like a filesystem at runtime.
+#
+# This is somewhat like frozen modules in python, but allows arbitrary files
+# to be used.
+
+from __future__ import print_function
+
+import argparse
+import os
+import subprocess
+import sys
+import types
+
+def create_zip(zip_filename, zip_dir):
+    abs_zip_filename = os.path.abspath(zip_filename)
+    save_cwd = os.getcwd()
+    os.chdir(zip_dir)
+    if os.path.exists(abs_zip_filename):
+        os.remove(abs_zip_filename)
+    subprocess.check_call(['zip', '-0', '-r', '-D', abs_zip_filename, '.'])
+    os.chdir(save_cwd)
+
+def create_c_from_file(c_filename, zip_filename):
+    with open(zip_filename, 'rb') as zip_file:
+        with open(c_filename, 'wb') as c_file:
+            print('#include <stdint.h>', file=c_file)
+            print('', file=c_file)
+            print('const uint8_t memzip_data[] = {', file=c_file)
+            while True:
+                buf = zip_file.read(16)
+                if not buf:
+                    break
+                print('   ', end='', file=c_file)
+                for byte in buf:
+                    if type(byte) is types.StringType:
+                        print(' 0x{:02x},'.format(ord(byte)), end='', file=c_file)
+                    else:
+                        print(' 0x{:02x},'.format(byte), end='', file=c_file)
+                print('', file=c_file)
+            print('};', file=c_file)
+
+def main():
+    parser = argparse.ArgumentParser(
+        prog='make-memzip.py',
+        usage='%(prog)s [options] [command]',
+        description='Generates a C source memzip file.'
+    )
+    parser.add_argument(
+        '-z', '--zip-file',
+        dest='zip_filename',
+        help='Specifies the name of the created zip file.',
+        default='memzip_files.zip'
+    )
+    parser.add_argument(
+        '-c', '--c-file',
+        dest='c_filename',
+        help='Specifies the name of the created C source file.',
+        default='memzip_files.c'
+    )
+    parser.add_argument(
+        dest='source_dir',
+        default='memzip_files'
+    )
+    args = parser.parse_args(sys.argv[1:])
+
+    print('args.zip_filename =', args.zip_filename)
+    print('args.c_filename =', args.c_filename)
+    print('args.source_dir =', args.source_dir)
+
+    create_zip(args.zip_filename, args.source_dir)
+    create_c_from_file(args.c_filename, args.zip_filename)
+
+if __name__ == "__main__":
+    main()
+
diff --git a/shared/memzip/memzip.c b/shared/memzip/memzip.c
new file mode 100644
index 000000000..3fbea8e1e
--- /dev/null
+++ b/shared/memzip/memzip.c
@@ -0,0 +1,106 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include "py/mpconfig.h"
+#include "py/misc.h"
+#include "memzip.h"
+
+extern uint8_t memzip_data[];
+
+const MEMZIP_FILE_HDR *memzip_find_file_header(const char *filename) {
+
+    const MEMZIP_FILE_HDR *file_hdr = (const MEMZIP_FILE_HDR *)memzip_data;
+    uint8_t *mem_data;
+
+    /* Zip file filenames don't have a leading /, so we strip it off */
+
+    if (*filename == '/') {
+        filename++;
+    }
+    while (file_hdr->signature == MEMZIP_FILE_HEADER_SIGNATURE) {
+        const char *file_hdr_filename = (const char *)&file_hdr[1];
+        mem_data = (uint8_t *)file_hdr_filename;
+        mem_data += file_hdr->filename_len;
+        mem_data += file_hdr->extra_len;
+        if (!strncmp(file_hdr_filename, filename, file_hdr->filename_len)) {
+            /* We found a match */
+            return file_hdr;
+        }
+        mem_data += file_hdr->uncompressed_size;
+        file_hdr = (const MEMZIP_FILE_HDR *)mem_data;
+    }
+    return NULL;
+}
+
+bool memzip_is_dir(const char *filename) {
+    const MEMZIP_FILE_HDR *file_hdr = (const MEMZIP_FILE_HDR *)memzip_data;
+    uint8_t *mem_data;
+
+    if (strcmp(filename, "/") == 0) {
+        // The root directory is a directory.
+        return true;
+    }
+
+    // Zip filenames don't have a leading /, so we strip it off
+    if (*filename == '/') {
+        filename++;
+    }
+    size_t filename_len = strlen(filename);
+
+    while (file_hdr->signature == MEMZIP_FILE_HEADER_SIGNATURE) {
+        const char *file_hdr_filename = (const char *)&file_hdr[1];
+        if (filename_len < file_hdr->filename_len &&
+            strncmp(file_hdr_filename, filename, filename_len) == 0 &&
+            file_hdr_filename[filename_len] == '/') {
+            return true;
+        }
+
+        mem_data = (uint8_t *)file_hdr_filename;
+        mem_data += file_hdr->filename_len;
+        mem_data += file_hdr->extra_len;
+        mem_data += file_hdr->uncompressed_size;
+        file_hdr = (const MEMZIP_FILE_HDR *)mem_data;
+    }
+    return NULL;
+
+}
+
+MEMZIP_RESULT memzip_locate(const char *filename, void **data, size_t *len)
+{
+    const MEMZIP_FILE_HDR *file_hdr = memzip_find_file_header(filename);
+    if (file_hdr == NULL) {
+        return MZ_NO_FILE;
+    }
+    if (file_hdr->compression_method != 0) {
+        return MZ_FILE_COMPRESSED;
+    }
+
+    uint8_t *mem_data;
+    mem_data = (uint8_t *)&file_hdr[1];
+    mem_data += file_hdr->filename_len;
+    mem_data += file_hdr->extra_len;
+
+    *data = mem_data;
+    *len = file_hdr->uncompressed_size;
+    return MZ_OK;
+}
+
+MEMZIP_RESULT memzip_stat(const char *path, MEMZIP_FILE_INFO *info) {
+    const MEMZIP_FILE_HDR *file_hdr = memzip_find_file_header(path);
+    if (file_hdr == NULL) {
+        if (memzip_is_dir(path)) {
+            info->file_size = 0;
+            info->last_mod_date = 0;
+            info->last_mod_time = 0;
+            info->is_dir = 1;
+            return MZ_OK;
+        }
+        return MZ_NO_FILE;
+    }
+    info->file_size = file_hdr->uncompressed_size;
+    info->last_mod_date = file_hdr->last_mod_date;
+    info->last_mod_time = file_hdr->last_mod_time;
+    info->is_dir = 0;
+
+    return MZ_OK;
+}
diff --git a/shared/memzip/memzip.h b/shared/memzip/memzip.h
new file mode 100644
index 000000000..667e2df7e
--- /dev/null
+++ b/shared/memzip/memzip.h
@@ -0,0 +1,83 @@
+#pragma pack(push, 1)
+
+#define MEMZIP_FILE_HEADER_SIGNATURE 0x04034b50
+typedef struct
+{
+    uint32_t    signature;
+    uint16_t    version;
+    uint16_t    flags;
+    uint16_t    compression_method;
+    uint16_t    last_mod_time;
+    uint16_t    last_mod_date;
+    uint32_t    crc32;
+    uint32_t    compressed_size;
+    uint32_t    uncompressed_size;
+    uint16_t    filename_len;
+    uint16_t    extra_len;
+
+    /* char     filename[filename_len]  */
+    /* uint8_t  extra[extra_len]        */
+
+} MEMZIP_FILE_HDR;
+
+#define MEMZIP_CENTRAL_DIRECTORY_SIGNATURE 0x02014b50
+typedef struct
+{
+    uint32_t    signature;
+    uint16_t    version_made_by;
+    uint16_t    version_read_with;
+    uint16_t    flags;
+    uint16_t    compression_method;
+    uint16_t    last_mod_time;
+    uint16_t    last_mod_date;
+    uint32_t    crc32;
+    uint32_t    compressed_size;
+    uint32_t    uncompressed_size;
+    uint16_t    filename_len;
+    uint16_t    extra_len;
+    uint16_t    disk_num;
+    uint16_t    internal_file_attributes;
+    uint32_t    external_file_attributes;
+    uint32_t    file_header_offset;
+
+    /* char     filename[filename_len]  */
+    /* uint8_t  extra[extra_len]        */
+
+} MEMZIP_CENTRAL_DIRECTORY_HDR;
+
+#define MEMZIP_END_OF_CENTRAL_DIRECTORY_SIGNATURE 0x06054b50
+typedef struct
+{
+    uint32_t    signature;
+    uint16_t    disk_num;
+    uint16_t    central_directory_disk;
+    uint16_t    num_central_directories_this_disk;
+    uint16_t    total_central_directories;
+    uint32_t    central_directory_size;
+    uint32_t    central_directory_offset;
+    uint16_t    comment_len;
+
+    /* char     comment[comment_len]    */
+
+} MEMZIP_END_OF_CENTRAL_DIRECTORY;
+
+#pragma pack(pop)
+
+typedef enum {
+    MZ_OK = 0,          /* (0) Succeeded */
+    MZ_NO_FILE,         /* (1) Could not find the file. */
+    MZ_FILE_COMPRESSED, /* (2) File is compressed (expecting uncompressed) */
+
+} MEMZIP_RESULT;
+
+typedef struct {
+    uint32_t    file_size;
+    uint16_t    last_mod_date;
+    uint16_t    last_mod_time;
+    uint8_t     is_dir;
+
+} MEMZIP_FILE_INFO;
+
+MEMZIP_RESULT memzip_locate(const char *filename, void **data, size_t *len);
+
+MEMZIP_RESULT memzip_stat(const char *path, MEMZIP_FILE_INFO *info);
diff --git a/shared/netutils/dhcpserver.c b/shared/netutils/dhcpserver.c
new file mode 100644
index 000000000..7f97ee6e4
--- /dev/null
+++ b/shared/netutils/dhcpserver.c
@@ -0,0 +1,304 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018-2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// For DHCP specs see:
+//  https://www.ietf.org/rfc/rfc2131.txt
+//  https://tools.ietf.org/html/rfc2132 -- DHCP Options and BOOTP Vendor Extensions
+
+#include <stdio.h>
+#include <string.h>
+#include "py/mperrno.h"
+#include "py/mphal.h"
+
+#if MICROPY_PY_LWIP
+
+#include "lib/netutils/dhcpserver.h"
+#include "lwip/udp.h"
+
+#define DHCPDISCOVER    (1)
+#define DHCPOFFER       (2)
+#define DHCPREQUEST     (3)
+#define DHCPDECLINE     (4)
+#define DHCPACK         (5)
+#define DHCPNACK        (6)
+#define DHCPRELEASE     (7)
+#define DHCPINFORM      (8)
+
+#define DHCP_OPT_PAD                (0)
+#define DHCP_OPT_SUBNET_MASK        (1)
+#define DHCP_OPT_ROUTER             (3)
+#define DHCP_OPT_DNS                (6)
+#define DHCP_OPT_HOST_NAME          (12)
+#define DHCP_OPT_REQUESTED_IP       (50)
+#define DHCP_OPT_IP_LEASE_TIME      (51)
+#define DHCP_OPT_MSG_TYPE           (53)
+#define DHCP_OPT_SERVER_ID          (54)
+#define DHCP_OPT_PARAM_REQUEST_LIST (55)
+#define DHCP_OPT_MAX_MSG_SIZE       (57)
+#define DHCP_OPT_VENDOR_CLASS_ID    (60)
+#define DHCP_OPT_CLIENT_ID          (61)
+#define DHCP_OPT_END                (255)
+
+#define PORT_DHCP_SERVER (67)
+#define PORT_DHCP_CLIENT (68)
+
+#define DEFAULT_DNS MAKE_IP4(8, 8, 8, 8)
+#define DEFAULT_LEASE_TIME_S (24 * 60 * 60) // in seconds
+
+#define MAC_LEN (6)
+#define MAKE_IP4(a, b, c, d) ((a) << 24 | (b) << 16 | (c) << 8 | (d))
+
+typedef struct {
+    uint8_t op; // message opcode
+    uint8_t htype; // hardware address type
+    uint8_t hlen; // hardware address length
+    uint8_t hops;
+    uint32_t xid; // transaction id, chosen by client
+    uint16_t secs; // client seconds elapsed
+    uint16_t flags;
+    uint8_t ciaddr[4]; // client IP address
+    uint8_t yiaddr[4]; // your IP address
+    uint8_t siaddr[4]; // next server IP address
+    uint8_t giaddr[4]; // relay agent IP address
+    uint8_t chaddr[16]; // client hardware address
+    uint8_t sname[64]; // server host name
+    uint8_t file[128]; // boot file name
+    uint8_t options[312]; // optional parameters, variable, starts with magic
+} dhcp_msg_t;
+
+static int dhcp_socket_new_dgram(struct udp_pcb **udp, void *cb_data, udp_recv_fn cb_udp_recv) {
+    // family is AF_INET
+    // type is SOCK_DGRAM
+
+    *udp = udp_new();
+    if (*udp == NULL) {
+        return -MP_ENOMEM;
+    }
+
+    // Register callback
+    udp_recv(*udp, cb_udp_recv, (void *)cb_data);
+
+    return 0; // success
+}
+
+static void dhcp_socket_free(struct udp_pcb **udp) {
+    if (*udp != NULL) {
+        udp_remove(*udp);
+        *udp = NULL;
+    }
+}
+
+static int dhcp_socket_bind(struct udp_pcb **udp, uint32_t ip, uint16_t port) {
+    ip_addr_t addr;
+    IP4_ADDR(&addr, ip >> 24 & 0xff, ip >> 16 & 0xff, ip >> 8 & 0xff, ip & 0xff);
+    // TODO convert lwIP errors to errno
+    return udp_bind(*udp, &addr, port);
+}
+
+static int dhcp_socket_sendto(struct udp_pcb **udp, const void *buf, size_t len, uint32_t ip, uint16_t port) {
+    if (len > 0xffff) {
+        len = 0xffff;
+    }
+
+    struct pbuf *p = pbuf_alloc(PBUF_TRANSPORT, len, PBUF_RAM);
+    if (p == NULL) {
+        return -MP_ENOMEM;
+    }
+
+    memcpy(p->payload, buf, len);
+
+    ip_addr_t dest;
+    IP4_ADDR(&dest, ip >> 24 & 0xff, ip >> 16 & 0xff, ip >> 8 & 0xff, ip & 0xff);
+    err_t err = udp_sendto(*udp, p, &dest, port);
+
+    pbuf_free(p);
+
+    if (err != ERR_OK) {
+        return err;
+    }
+
+    return len;
+}
+
+static uint8_t *opt_find(uint8_t *opt, uint8_t cmd) {
+    for (int i = 0; i < 308 && opt[i] != DHCP_OPT_END;) {
+        if (opt[i] == cmd) {
+            return &opt[i];
+        }
+        i += 2 + opt[i + 1];
+    }
+    return NULL;
+}
+
+static void opt_write_n(uint8_t **opt, uint8_t cmd, size_t n, void *data) {
+    uint8_t *o = *opt;
+    *o++ = cmd;
+    *o++ = n;
+    memcpy(o, data, n);
+    *opt = o + n;
+}
+
+static void opt_write_u8(uint8_t **opt, uint8_t cmd, uint8_t val) {
+    uint8_t *o = *opt;
+    *o++ = cmd;
+    *o++ = 1;
+    *o++ = val;
+    *opt = o;
+}
+
+static void opt_write_u32(uint8_t **opt, uint8_t cmd, uint32_t val) {
+    uint8_t *o = *opt;
+    *o++ = cmd;
+    *o++ = 4;
+    *o++ = val >> 24;
+    *o++ = val >> 16;
+    *o++ = val >> 8;
+    *o++ = val;
+    *opt = o;
+}
+
+static void dhcp_server_process(void *arg, struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t *src_addr, u16_t src_port) {
+    dhcp_server_t *d = arg;
+    (void)upcb;
+    (void)src_addr;
+    (void)src_port;
+
+    // This is around 548 bytes
+    dhcp_msg_t dhcp_msg;
+
+    #define DHCP_MIN_SIZE (240 + 3)
+    if (p->tot_len < DHCP_MIN_SIZE) {
+        goto ignore_request;
+    }
+
+    size_t len = pbuf_copy_partial(p, &dhcp_msg, sizeof(dhcp_msg), 0);
+    if (len < DHCP_MIN_SIZE) {
+        goto ignore_request;
+    }
+
+    dhcp_msg.op = DHCPOFFER;
+    memcpy(&dhcp_msg.yiaddr, &d->ip.addr, 4);
+
+    uint8_t *opt = (uint8_t *)&dhcp_msg.options;
+    opt += 4; // assume magic cookie: 99, 130, 83, 99
+
+    switch (opt[2]) {
+        case DHCPDISCOVER: {
+            int yi = DHCPS_MAX_IP;
+            for (int i = 0; i < DHCPS_MAX_IP; ++i) {
+                if (memcmp(d->lease[i].mac, dhcp_msg.chaddr, MAC_LEN) == 0) {
+                    // MAC match, use this IP address
+                    yi = i;
+                    break;
+                }
+                if (yi == DHCPS_MAX_IP) {
+                    // Look for a free IP address
+                    if (memcmp(d->lease[i].mac, "\x00\x00\x00\x00\x00\x00", MAC_LEN) == 0) {
+                        // IP available
+                        yi = i;
+                    }
+                    uint32_t expiry = d->lease[i].expiry << 16 | 0xffff;
+                    if ((int32_t)(expiry - mp_hal_ticks_ms()) < 0) {
+                        // IP expired, reuse it
+                        memset(d->lease[i].mac, 0, MAC_LEN);
+                        yi = i;
+                    }
+                }
+            }
+            if (yi == DHCPS_MAX_IP) {
+                // No more IP addresses left
+                goto ignore_request;
+            }
+            dhcp_msg.yiaddr[3] = DHCPS_BASE_IP + yi;
+            opt_write_u8(&opt, DHCP_OPT_MSG_TYPE, DHCPOFFER);
+            break;
+        }
+
+        case DHCPREQUEST: {
+            uint8_t *o = opt_find(opt, DHCP_OPT_REQUESTED_IP);
+            if (o == NULL) {
+                // Should be NACK
+                goto ignore_request;
+            }
+            if (memcmp(o + 2, &d->ip.addr, 3) != 0) {
+                // Should be NACK
+                goto ignore_request;
+            }
+            uint8_t yi = o[5] - DHCPS_BASE_IP;
+            if (yi >= DHCPS_MAX_IP) {
+                // Should be NACK
+                goto ignore_request;
+            }
+            if (memcmp(d->lease[yi].mac, dhcp_msg.chaddr, MAC_LEN) == 0) {
+                // MAC match, ok to use this IP address
+            } else if (memcmp(d->lease[yi].mac, "\x00\x00\x00\x00\x00\x00", MAC_LEN) == 0) {
+                // IP unused, ok to use this IP address
+                memcpy(d->lease[yi].mac, dhcp_msg.chaddr, MAC_LEN);
+            } else {
+                // IP already in use
+                // Should be NACK
+                goto ignore_request;
+            }
+            d->lease[yi].expiry = (mp_hal_ticks_ms() + DEFAULT_LEASE_TIME_S * 1000) >> 16;
+            dhcp_msg.yiaddr[3] = DHCPS_BASE_IP + yi;
+            opt_write_u8(&opt, DHCP_OPT_MSG_TYPE, DHCPACK);
+            printf("DHCPS: client connected: MAC=%02x:%02x:%02x:%02x:%02x:%02x IP=%u.%u.%u.%u\n",
+                dhcp_msg.chaddr[0], dhcp_msg.chaddr[1], dhcp_msg.chaddr[2], dhcp_msg.chaddr[3], dhcp_msg.chaddr[4], dhcp_msg.chaddr[5],
+                dhcp_msg.yiaddr[0], dhcp_msg.yiaddr[1], dhcp_msg.yiaddr[2], dhcp_msg.yiaddr[3]);
+            break;
+        }
+
+        default:
+            goto ignore_request;
+    }
+
+    opt_write_n(&opt, DHCP_OPT_SERVER_ID, 4, &d->ip.addr);
+    opt_write_n(&opt, DHCP_OPT_SUBNET_MASK, 4, &d->nm.addr);
+    opt_write_n(&opt, DHCP_OPT_ROUTER, 4, &d->ip.addr); // aka gateway; can have mulitple addresses
+    opt_write_u32(&opt, DHCP_OPT_DNS, DEFAULT_DNS); // can have mulitple addresses
+    opt_write_u32(&opt, DHCP_OPT_IP_LEASE_TIME, DEFAULT_LEASE_TIME_S);
+    *opt++ = DHCP_OPT_END;
+    dhcp_socket_sendto(&d->udp, &dhcp_msg, opt - (uint8_t *)&dhcp_msg, 0xffffffff, PORT_DHCP_CLIENT);
+
+ignore_request:
+    pbuf_free(p);
+}
+
+void dhcp_server_init(dhcp_server_t *d, ip_addr_t *ip, ip_addr_t *nm) {
+    ip_addr_copy(d->ip, *ip);
+    ip_addr_copy(d->nm, *nm);
+    memset(d->lease, 0, sizeof(d->lease));
+    if (dhcp_socket_new_dgram(&d->udp, d, dhcp_server_process) != 0) {
+        return;
+    }
+    dhcp_socket_bind(&d->udp, 0, PORT_DHCP_SERVER);
+}
+
+void dhcp_server_deinit(dhcp_server_t *d) {
+    dhcp_socket_free(&d->udp);
+}
+
+#endif // MICROPY_PY_LWIP
diff --git a/shared/netutils/dhcpserver.h b/shared/netutils/dhcpserver.h
new file mode 100644
index 000000000..2349d2ea4
--- /dev/null
+++ b/shared/netutils/dhcpserver.h
@@ -0,0 +1,49 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018-2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_NETUTILS_DHCPSERVER_H
+#define MICROPY_INCLUDED_LIB_NETUTILS_DHCPSERVER_H
+
+#include "lwip/ip_addr.h"
+
+#define DHCPS_BASE_IP (16)
+#define DHCPS_MAX_IP (8)
+
+typedef struct _dhcp_server_lease_t {
+    uint8_t mac[6];
+    uint16_t expiry;
+} dhcp_server_lease_t;
+
+typedef struct _dhcp_server_t {
+    ip_addr_t ip;
+    ip_addr_t nm;
+    dhcp_server_lease_t lease[DHCPS_MAX_IP];
+    struct udp_pcb *udp;
+} dhcp_server_t;
+
+void dhcp_server_init(dhcp_server_t *d, ip_addr_t *ip, ip_addr_t *nm);
+void dhcp_server_deinit(dhcp_server_t *d);
+
+#endif // MICROPY_INCLUDED_LIB_NETUTILS_DHCPSERVER_H
diff --git a/shared/netutils/netutils.c b/shared/netutils/netutils.c
new file mode 100644
index 000000000..40fbd5bca
--- /dev/null
+++ b/shared/netutils/netutils.c
@@ -0,0 +1,94 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2015 Daniel Campora
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "py/runtime.h"
+#include "lib/netutils/netutils.h"
+
+// Takes an array with a raw IPv4 address and returns something like '192.168.0.1'.
+mp_obj_t netutils_format_ipv4_addr(uint8_t *ip, netutils_endian_t endian) {
+    char ip_str[16];
+    mp_uint_t ip_len;
+    if (endian == NETUTILS_LITTLE) {
+        ip_len = snprintf(ip_str, 16, "%u.%u.%u.%u", ip[3], ip[2], ip[1], ip[0]);
+    } else {
+        ip_len = snprintf(ip_str, 16, "%u.%u.%u.%u", ip[0], ip[1], ip[2], ip[3]);
+    }
+    return mp_obj_new_str(ip_str, ip_len);
+}
+
+// Takes an array with a raw IP address, and a port, and returns a net-address
+// tuple such as ('192.168.0.1', 8080).
+mp_obj_t netutils_format_inet_addr(uint8_t *ip, mp_uint_t port, netutils_endian_t endian) {
+    mp_obj_t tuple[2] = {
+        tuple[0] = netutils_format_ipv4_addr(ip, endian),
+        tuple[1] = mp_obj_new_int(port),
+    };
+    return mp_obj_new_tuple(2, tuple);
+}
+
+void netutils_parse_ipv4_addr(mp_obj_t addr_in, uint8_t *out_ip, netutils_endian_t endian) {
+    size_t addr_len;
+    const char *addr_str = mp_obj_str_get_data(addr_in, &addr_len);
+    if (addr_len == 0) {
+        // special case of no address given
+        memset(out_ip, 0, NETUTILS_IPV4ADDR_BUFSIZE);
+        return;
+    }
+    const char *s = addr_str;
+    const char *s_top = addr_str + addr_len;
+    for (mp_uint_t i = 3; ; i--) {
+        mp_uint_t val = 0;
+        for (; s < s_top && *s != '.'; s++) {
+            val = val * 10 + *s - '0';
+        }
+        if (endian == NETUTILS_LITTLE) {
+            out_ip[i] = val;
+        } else {
+            out_ip[NETUTILS_IPV4ADDR_BUFSIZE - 1 - i] = val;
+        }
+        if (i == 0 && s == s_top) {
+            return;
+        } else if (i > 0 && s < s_top && *s == '.') {
+            s++;
+        } else {
+            mp_raise_ValueError(MP_ERROR_TEXT("invalid arguments"));
+        }
+    }
+}
+
+// Takes an address of the form ('192.168.0.1', 8080), returns the port and
+// puts IP in out_ip (which must take at least IPADDR_BUF_SIZE bytes).
+mp_uint_t netutils_parse_inet_addr(mp_obj_t addr_in, uint8_t *out_ip, netutils_endian_t endian) {
+    mp_obj_t *addr_items;
+    mp_obj_get_array_fixed_n(addr_in, 2, &addr_items);
+    netutils_parse_ipv4_addr(addr_items[0], out_ip, endian);
+    return mp_obj_get_int(addr_items[1]);
+}
diff --git a/shared/netutils/netutils.h b/shared/netutils/netutils.h
new file mode 100644
index 000000000..926133785
--- /dev/null
+++ b/shared/netutils/netutils.h
@@ -0,0 +1,56 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2015 Daniel Campora
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_NETUTILS_NETUTILS_H
+#define MICROPY_INCLUDED_LIB_NETUTILS_NETUTILS_H
+
+#define NETUTILS_IPV4ADDR_BUFSIZE    4
+
+#define NETUTILS_TRACE_IS_TX        (0x0001)
+#define NETUTILS_TRACE_PAYLOAD      (0x0002)
+#define NETUTILS_TRACE_NEWLINE      (0x0004)
+
+typedef enum _netutils_endian_t {
+    NETUTILS_LITTLE,
+    NETUTILS_BIG,
+} netutils_endian_t;
+
+// Takes an array with a raw IPv4 address and returns something like '192.168.0.1'.
+mp_obj_t netutils_format_ipv4_addr(uint8_t *ip, netutils_endian_t endian);
+
+// Takes an array with a raw IP address, and a port, and returns a net-address
+// tuple such as ('192.168.0.1', 8080).
+mp_obj_t netutils_format_inet_addr(uint8_t *ip, mp_uint_t port, netutils_endian_t endian);
+
+void netutils_parse_ipv4_addr(mp_obj_t addr_in, uint8_t *out_ip, netutils_endian_t endian);
+
+// Takes an address of the form ('192.168.0.1', 8080), returns the port and
+// puts IP in out_ip (which must take at least IPADDR_BUF_SIZE bytes).
+mp_uint_t netutils_parse_inet_addr(mp_obj_t addr_in, uint8_t *out_ip, netutils_endian_t endian);
+
+void netutils_ethernet_trace(const mp_print_t *print, size_t len, const uint8_t *buf, unsigned int flags);
+
+#endif // MICROPY_INCLUDED_LIB_NETUTILS_NETUTILS_H
diff --git a/shared/netutils/trace.c b/shared/netutils/trace.c
new file mode 100644
index 000000000..1610966c2
--- /dev/null
+++ b/shared/netutils/trace.c
@@ -0,0 +1,170 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/mphal.h"
+#include "lib/netutils/netutils.h"
+
+static uint32_t get_be16(const uint8_t *buf) {
+    return buf[0] << 8 | buf[1];
+}
+
+static uint32_t get_be32(const uint8_t *buf) {
+    return buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3];
+}
+
+static void dump_hex_bytes(const mp_print_t *print, size_t len, const uint8_t *buf) {
+    for (size_t i = 0; i < len; ++i) {
+        mp_printf(print, " %02x", buf[i]);
+    }
+}
+
+static const char *ethertype_str(uint16_t type) {
+    // A value between 0x0000 - 0x05dc (inclusive) indicates a length, not type
+    switch (type) {
+        case 0x0800:
+            return "IPv4";
+        case 0x0806:
+            return "ARP";
+        case 0x86dd:
+            return "IPv6";
+        default:
+            return NULL;
+    }
+}
+
+void netutils_ethernet_trace(const mp_print_t *print, size_t len, const uint8_t *buf, unsigned int flags) {
+    mp_printf(print, "[% 8d] ETH%cX len=%u", mp_hal_ticks_ms(), flags & NETUTILS_TRACE_IS_TX ? 'T' : 'R', len);
+    mp_printf(print, " dst=%02x:%02x:%02x:%02x:%02x:%02x", buf[0], buf[1], buf[2], buf[3], buf[4], buf[5]);
+    mp_printf(print, " src=%02x:%02x:%02x:%02x:%02x:%02x", buf[6], buf[7], buf[8], buf[9], buf[10], buf[11]);
+
+    const char *ethertype = ethertype_str(buf[12] << 8 | buf[13]);
+    if (ethertype) {
+        mp_printf(print, " type=%s", ethertype);
+    } else {
+        mp_printf(print, " type=0x%04x", buf[12] << 8 | buf[13]);
+    }
+    if (len > 14) {
+        len -= 14;
+        buf += 14;
+        if (buf[-2] == 0x08 && buf[-1] == 0x00 && buf[0] == 0x45) {
+            // IPv4 packet
+            len = get_be16(buf + 2);
+            mp_printf(print, " srcip=%u.%u.%u.%u dstip=%u.%u.%u.%u",
+                buf[12], buf[13], buf[14], buf[15],
+                buf[16], buf[17], buf[18], buf[19]);
+            uint8_t prot = buf[9];
+            buf += 20;
+            len -= 20;
+            if (prot == 6) {
+                // TCP packet
+                uint16_t srcport = get_be16(buf);
+                uint16_t dstport = get_be16(buf + 2);
+                uint32_t seqnum = get_be32(buf + 4);
+                uint32_t acknum = get_be32(buf + 8);
+                uint16_t dataoff_flags = get_be16(buf + 12);
+                uint16_t winsz = get_be16(buf + 14);
+                mp_printf(print, " TCP srcport=%u dstport=%u seqnum=%u acknum=%u dataoff=%u flags=%x winsz=%u",
+                    srcport, dstport, (unsigned)seqnum, (unsigned)acknum, dataoff_flags >> 12, dataoff_flags & 0x1ff, winsz);
+                buf += 20;
+                len -= 20;
+                if (dataoff_flags >> 12 > 5) {
+                    mp_printf(print, " opts=");
+                    size_t opts_len = ((dataoff_flags >> 12) - 5) * 4;
+                    dump_hex_bytes(print, opts_len, buf);
+                    buf += opts_len;
+                    len -= opts_len;
+                }
+            } else if (prot == 17) {
+                // UDP packet
+                uint16_t srcport = get_be16(buf);
+                uint16_t dstport = get_be16(buf + 2);
+                mp_printf(print, " UDP srcport=%u dstport=%u", srcport, dstport);
+                len = get_be16(buf + 4);
+                buf += 8;
+                if ((srcport == 67 && dstport == 68) || (srcport == 68 && dstport == 67)) {
+                    // DHCP
+                    if (srcport == 67) {
+                        mp_printf(print, " DHCPS");
+                    } else {
+                        mp_printf(print, " DHCPC");
+                    }
+                    dump_hex_bytes(print, 12 + 16 + 16 + 64, buf);
+                    size_t n = 12 + 16 + 16 + 64 + 128;
+                    len -= n;
+                    buf += n;
+                    mp_printf(print, " opts:");
+                    switch (buf[6]) {
+                        case 1:
+                            mp_printf(print, " DISCOVER");
+                            break;
+                        case 2:
+                            mp_printf(print, " OFFER");
+                            break;
+                        case 3:
+                            mp_printf(print, " REQUEST");
+                            break;
+                        case 4:
+                            mp_printf(print, " DECLINE");
+                            break;
+                        case 5:
+                            mp_printf(print, " ACK");
+                            break;
+                        case 6:
+                            mp_printf(print, " NACK");
+                            break;
+                        case 7:
+                            mp_printf(print, " RELEASE");
+                            break;
+                        case 8:
+                            mp_printf(print, " INFORM");
+                            break;
+                    }
+                }
+            } else {
+                // Non-UDP packet
+                mp_printf(print, " prot=%u", prot);
+            }
+        } else if (buf[-2] == 0x86 && buf[-1] == 0xdd && (buf[0] >> 4) == 6) {
+            // IPv6 packet
+            uint32_t h = get_be32(buf);
+            uint16_t l = get_be16(buf + 4);
+            mp_printf(print, " tclass=%u flow=%u len=%u nexthdr=%u hoplimit=%u", (unsigned)((h >> 20) & 0xff), (unsigned)(h & 0xfffff), l, buf[6], buf[7]);
+            mp_printf(print, " srcip=");
+            dump_hex_bytes(print, 16, buf + 8);
+            mp_printf(print, " dstip=");
+            dump_hex_bytes(print, 16, buf + 24);
+            buf += 40;
+            len -= 40;
+        }
+        if (flags & NETUTILS_TRACE_PAYLOAD) {
+            mp_printf(print, " data=");
+            dump_hex_bytes(print, len, buf);
+        }
+    }
+    if (flags & NETUTILS_TRACE_NEWLINE) {
+        mp_printf(print, "\n");
+    }
+}
diff --git a/shared/readline/readline.c b/shared/readline/readline.c
new file mode 100644
index 000000000..296c8aa4a
--- /dev/null
+++ b/shared/readline/readline.c
@@ -0,0 +1,534 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "py/mpstate.h"
+#include "py/repl.h"
+#include "py/mphal.h"
+#include "lib/mp-readline/readline.h"
+
+#if 0 // print debugging info
+#define DEBUG_PRINT (1)
+#define DEBUG_printf printf
+#else // don't print debugging info
+#define DEBUG_printf(...) (void)0
+#endif
+
+#define READLINE_HIST_SIZE (MP_ARRAY_SIZE(MP_STATE_PORT(readline_hist)))
+
+enum { ESEQ_NONE, ESEQ_ESC, ESEQ_ESC_BRACKET, ESEQ_ESC_BRACKET_DIGIT, ESEQ_ESC_O };
+
+void readline_init0(void) {
+    memset(MP_STATE_PORT(readline_hist), 0, READLINE_HIST_SIZE * sizeof(const char*));
+}
+
+STATIC char *str_dup_maybe(const char *str) {
+    uint32_t len = strlen(str);
+    char *s2 = m_new_maybe(char, len + 1);
+    if (s2 == NULL) {
+        return NULL;
+    }
+    memcpy(s2, str, len + 1);
+    return s2;
+}
+
+// By default assume terminal which implements VT100 commands...
+#ifndef MICROPY_HAL_HAS_VT100
+#define MICROPY_HAL_HAS_VT100 (1)
+#endif
+
+// ...and provide the implementation using them
+#if MICROPY_HAL_HAS_VT100
+STATIC void mp_hal_move_cursor_back(uint pos) {
+    if (pos <= 4) {
+        // fast path for most common case of 1 step back
+        mp_hal_stdout_tx_strn("\b\b\b\b", pos);
+    } else {
+        char vt100_command[6];
+        // snprintf needs space for the terminating null character
+        int n = snprintf(&vt100_command[0], sizeof(vt100_command), "\x1b[%u", pos);
+        if (n > 0) {
+            assert((unsigned)n < sizeof(vt100_command));
+            vt100_command[n] = 'D'; // replace null char
+            mp_hal_stdout_tx_strn(vt100_command, n + 1);
+        }
+    }
+}
+
+STATIC void mp_hal_erase_line_from_cursor(uint n_chars_to_erase) {
+    (void)n_chars_to_erase;
+    mp_hal_stdout_tx_strn("\x1b[K", 3);
+}
+#endif
+
+typedef struct _readline_t {
+    vstr_t *line;
+    size_t orig_line_len;
+    int escape_seq;
+    int hist_cur;
+    size_t cursor_pos;
+    char escape_seq_buf[1];
+    const char *prompt;
+} readline_t;
+
+STATIC readline_t rl;
+
+#if MICROPY_REPL_EMACS_WORDS_MOVE
+STATIC size_t cursor_count_word(int forward) {
+    const char *line_buf = vstr_str(rl.line);
+    size_t pos = rl.cursor_pos;
+    bool in_word = false;
+
+    for (;;) {
+        // if moving backwards and we've reached 0... break
+        if (!forward && pos == 0) {
+            break;
+        }
+        // or if moving forwards and we've reached to the end of line... break
+        else if (forward && pos == vstr_len(rl.line)) {
+            break;
+        }
+
+        if (unichar_isalnum(line_buf[pos + (forward - 1)])) {
+            in_word = true;
+        } else if (in_word) {
+            break;
+        }
+
+        pos += forward ? forward : -1;
+    }
+
+    return forward ? pos - rl.cursor_pos : rl.cursor_pos - pos;
+}
+#endif
+
+int readline_process_char(int c) {
+    size_t last_line_len = rl.line->len;
+    int redraw_step_back = 0;
+    bool redraw_from_cursor = false;
+    int redraw_step_forward = 0;
+    if (rl.escape_seq == ESEQ_NONE) {
+        if (CHAR_CTRL_A <= c && c <= CHAR_CTRL_E && vstr_len(rl.line) == rl.orig_line_len) {
+            // control character with empty line
+            return c;
+        } else if (c == CHAR_CTRL_A) {
+            // CTRL-A with non-empty line is go-to-start-of-line
+            goto home_key;
+        #if MICROPY_REPL_EMACS_KEYS
+        } else if (c == CHAR_CTRL_B) {
+            // CTRL-B with non-empty line is go-back-one-char
+            goto left_arrow_key;
+        #endif
+        } else if (c == CHAR_CTRL_C) {
+            // CTRL-C with non-empty line is cancel
+            return c;
+        #if MICROPY_REPL_EMACS_KEYS
+        } else if (c == CHAR_CTRL_D) {
+            // CTRL-D with non-empty line is delete-at-cursor
+            goto delete_key;
+        #endif
+        } else if (c == CHAR_CTRL_E) {
+            // CTRL-E is go-to-end-of-line
+            goto end_key;
+        #if MICROPY_REPL_EMACS_KEYS
+        } else if (c == CHAR_CTRL_F) {
+            // CTRL-F with non-empty line is go-forward-one-char
+            goto right_arrow_key;
+        } else if (c == CHAR_CTRL_K) {
+            // CTRL-K is kill from cursor to end-of-line, inclusive
+            vstr_cut_tail_bytes(rl.line, last_line_len - rl.cursor_pos);
+            // set redraw parameters
+            redraw_from_cursor = true;
+        } else if (c == CHAR_CTRL_N) {
+            // CTRL-N is go to next line in history
+            goto down_arrow_key;
+        } else if (c == CHAR_CTRL_P) {
+            // CTRL-P is go to previous line in history
+            goto up_arrow_key;
+        } else if (c == CHAR_CTRL_U) {
+            // CTRL-U is kill from beginning-of-line up to cursor
+            vstr_cut_out_bytes(rl.line, rl.orig_line_len, rl.cursor_pos - rl.orig_line_len);
+            // set redraw parameters
+            redraw_step_back = rl.cursor_pos - rl.orig_line_len;
+            redraw_from_cursor = true;
+        #endif
+        #if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+        } else if (c == CHAR_CTRL_W) {
+            goto backward_kill_word;
+        #endif
+        } else if (c == '\r') {
+            // newline
+            mp_hal_stdout_tx_str("\r\n");
+            readline_push_history(vstr_null_terminated_str(rl.line) + rl.orig_line_len);
+            return 0;
+        } else if (c == 27) {
+            // escape sequence
+            rl.escape_seq = ESEQ_ESC;
+        } else if (c == 8 || c == 127) {
+            // backspace/delete
+            if (rl.cursor_pos > rl.orig_line_len) {
+                // work out how many chars to backspace
+                #if MICROPY_REPL_AUTO_INDENT
+                int nspace = 0;
+                for (size_t i = rl.orig_line_len; i < rl.cursor_pos; i++) {
+                    if (rl.line->buf[i] != ' ') {
+                        nspace = 0;
+                        break;
+                    }
+                    nspace += 1;
+                }
+                if (nspace < 4) {
+                    nspace = 1;
+                } else {
+                    nspace = 4;
+                }
+                #else
+                int nspace = 1;
+                #endif
+
+                // do the backspace
+                vstr_cut_out_bytes(rl.line, rl.cursor_pos - nspace, nspace);
+                // set redraw parameters
+                redraw_step_back = nspace;
+                redraw_from_cursor = true;
+            }
+        #if MICROPY_HELPER_REPL
+        } else if (c == 9) {
+            // tab magic
+            const char *compl_str;
+            size_t compl_len = mp_repl_autocomplete(rl.line->buf + rl.orig_line_len, rl.cursor_pos - rl.orig_line_len, &mp_plat_print, &compl_str);
+            if (compl_len == 0) {
+                // no match
+            } else if (compl_len == (size_t)(-1)) {
+                // many matches
+                mp_hal_stdout_tx_str(rl.prompt);
+                mp_hal_stdout_tx_strn(rl.line->buf + rl.orig_line_len, rl.cursor_pos - rl.orig_line_len);
+                redraw_from_cursor = true;
+            } else {
+                // one match
+                for (size_t i = 0; i < compl_len; ++i) {
+                    vstr_ins_byte(rl.line, rl.cursor_pos + i, *compl_str++);
+                }
+                // set redraw parameters
+                redraw_from_cursor = true;
+                redraw_step_forward = compl_len;
+            }
+        #endif
+        } else if (32 <= c && c <= 126) {
+            // printable character
+            vstr_ins_char(rl.line, rl.cursor_pos, c);
+            // set redraw parameters
+            redraw_from_cursor = true;
+            redraw_step_forward = 1;
+        }
+    } else if (rl.escape_seq == ESEQ_ESC) {
+        switch (c) {
+            case '[':
+                rl.escape_seq = ESEQ_ESC_BRACKET;
+                break;
+            case 'O':
+                rl.escape_seq = ESEQ_ESC_O;
+                break;
+            #if MICROPY_REPL_EMACS_WORDS_MOVE
+            case 'b':
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+backward_word:
+#endif
+                redraw_step_back = cursor_count_word(0);
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 'f':
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+forward_word:
+#endif
+                redraw_step_forward = cursor_count_word(1);
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 'd':
+                vstr_cut_out_bytes(rl.line, rl.cursor_pos, cursor_count_word(1));
+                redraw_from_cursor = true;
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 127:
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+backward_kill_word:
+#endif
+                redraw_step_back = cursor_count_word(0);
+                vstr_cut_out_bytes(rl.line, rl.cursor_pos - redraw_step_back, redraw_step_back);
+                redraw_from_cursor = true;
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            #endif
+            default:
+                DEBUG_printf("(ESC %d)", c);
+                rl.escape_seq = ESEQ_NONE;
+                break;
+        }
+    } else if (rl.escape_seq == ESEQ_ESC_BRACKET) {
+        if ('0' <= c && c <= '9') {
+            rl.escape_seq = ESEQ_ESC_BRACKET_DIGIT;
+            rl.escape_seq_buf[0] = c;
+        } else {
+            rl.escape_seq = ESEQ_NONE;
+            if (c == 'A') {
+#if MICROPY_REPL_EMACS_KEYS
+up_arrow_key:
+#endif
+                // up arrow
+                if (rl.hist_cur + 1 < (int)READLINE_HIST_SIZE && MP_STATE_PORT(readline_hist)[rl.hist_cur + 1] != NULL) {
+                    // increase hist num
+                    rl.hist_cur += 1;
+                    // set line to history
+                    rl.line->len = rl.orig_line_len;
+                    vstr_add_str(rl.line, MP_STATE_PORT(readline_hist)[rl.hist_cur]);
+                    // set redraw parameters
+                    redraw_step_back = rl.cursor_pos - rl.orig_line_len;
+                    redraw_from_cursor = true;
+                    redraw_step_forward = rl.line->len - rl.orig_line_len;
+                }
+            } else if (c == 'B') {
+#if MICROPY_REPL_EMACS_KEYS
+down_arrow_key:
+#endif
+                // down arrow
+                if (rl.hist_cur >= 0) {
+                    // decrease hist num
+                    rl.hist_cur -= 1;
+                    // set line to history
+                    vstr_cut_tail_bytes(rl.line, rl.line->len - rl.orig_line_len);
+                    if (rl.hist_cur >= 0) {
+                        vstr_add_str(rl.line, MP_STATE_PORT(readline_hist)[rl.hist_cur]);
+                    }
+                    // set redraw parameters
+                    redraw_step_back = rl.cursor_pos - rl.orig_line_len;
+                    redraw_from_cursor = true;
+                    redraw_step_forward = rl.line->len - rl.orig_line_len;
+                }
+            } else if (c == 'C') {
+#if MICROPY_REPL_EMACS_KEYS
+right_arrow_key:
+#endif
+                // right arrow
+                if (rl.cursor_pos < rl.line->len) {
+                    redraw_step_forward = 1;
+                }
+            } else if (c == 'D') {
+#if MICROPY_REPL_EMACS_KEYS
+left_arrow_key:
+#endif
+                // left arrow
+                if (rl.cursor_pos > rl.orig_line_len) {
+                    redraw_step_back = 1;
+                }
+            } else if (c == 'H') {
+                // home
+                goto home_key;
+            } else if (c == 'F') {
+                // end
+                goto end_key;
+            } else {
+                DEBUG_printf("(ESC [ %d)", c);
+            }
+        }
+    } else if (rl.escape_seq == ESEQ_ESC_BRACKET_DIGIT) {
+        if (c == '~') {
+            if (rl.escape_seq_buf[0] == '1' || rl.escape_seq_buf[0] == '7') {
+home_key:
+                redraw_step_back = rl.cursor_pos - rl.orig_line_len;
+            } else if (rl.escape_seq_buf[0] == '4' || rl.escape_seq_buf[0] == '8') {
+end_key:
+                redraw_step_forward = rl.line->len - rl.cursor_pos;
+            } else if (rl.escape_seq_buf[0] == '3') {
+                // delete
+#if MICROPY_REPL_EMACS_KEYS
+delete_key:
+#endif
+                if (rl.cursor_pos < rl.line->len) {
+                    vstr_cut_out_bytes(rl.line, rl.cursor_pos, 1);
+                    redraw_from_cursor = true;
+                }
+            } else {
+                DEBUG_printf("(ESC [ %c %d)", rl.escape_seq_buf[0], c);
+            }
+        #if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+        } else if (c == ';' && rl.escape_seq_buf[0] == '1') {
+            // ';' is used to separate parameters. so first parameter was '1',
+            // that's used for sequences like ctrl+left, which we will try to parse.
+            // escape_seq state is reset back to ESEQ_ESC_BRACKET, as if we've just received
+            // the opening bracket, because more parameters are to come.
+            // we don't track the parameters themselves to keep low on logic and code size. that
+            // might be required in the future if more complex sequences are added.
+            rl.escape_seq = ESEQ_ESC_BRACKET;
+            // goto away from the state-machine, as rl.escape_seq will be overridden.
+            goto redraw;
+        } else if (rl.escape_seq_buf[0] == '5' && c == 'C') {
+            // ctrl+right
+            goto forward_word;
+        } else if (rl.escape_seq_buf[0] == '5' && c == 'D') {
+            // ctrl+left
+            goto backward_word;
+        #endif
+        } else {
+            DEBUG_printf("(ESC [ %c %d)", rl.escape_seq_buf[0], c);
+        }
+        rl.escape_seq = ESEQ_NONE;
+    } else if (rl.escape_seq == ESEQ_ESC_O) {
+        switch (c) {
+            case 'H':
+                goto home_key;
+            case 'F':
+                goto end_key;
+            default:
+                DEBUG_printf("(ESC O %d)", c);
+                rl.escape_seq = ESEQ_NONE;
+        }
+    } else {
+        rl.escape_seq = ESEQ_NONE;
+    }
+
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+redraw:
+#endif
+
+    // redraw command prompt, efficiently
+    if (redraw_step_back > 0) {
+        mp_hal_move_cursor_back(redraw_step_back);
+        rl.cursor_pos -= redraw_step_back;
+    }
+    if (redraw_from_cursor) {
+        if (rl.line->len < last_line_len) {
+            // erase old chars
+            mp_hal_erase_line_from_cursor(last_line_len - rl.cursor_pos);
+        }
+        // draw new chars
+        mp_hal_stdout_tx_strn(rl.line->buf + rl.cursor_pos, rl.line->len - rl.cursor_pos);
+        // move cursor forward if needed (already moved forward by length of line, so move it back)
+        mp_hal_move_cursor_back(rl.line->len - (rl.cursor_pos + redraw_step_forward));
+        rl.cursor_pos += redraw_step_forward;
+    } else if (redraw_step_forward > 0) {
+        // draw over old chars to move cursor forwards
+        mp_hal_stdout_tx_strn(rl.line->buf + rl.cursor_pos, redraw_step_forward);
+        rl.cursor_pos += redraw_step_forward;
+    }
+
+    return -1;
+}
+
+#if MICROPY_REPL_AUTO_INDENT
+STATIC void readline_auto_indent(void) {
+    vstr_t *line = rl.line;
+    if (line->len > 1 && line->buf[line->len - 1] == '\n') {
+        int i;
+        for (i = line->len - 1; i > 0; i--) {
+            if (line->buf[i - 1] == '\n') {
+                break;
+            }
+        }
+        size_t j;
+        for (j = i; j < line->len; j++) {
+            if (line->buf[j] != ' ') {
+                break;
+            }
+        }
+        // i=start of line; j=first non-space
+        if (i > 0 && j + 1 == line->len) {
+            // previous line is not first line and is all spaces
+            for (size_t k = i - 1; k > 0; --k) {
+                if (line->buf[k - 1] == '\n') {
+                    // don't auto-indent if last 2 lines are all spaces
+                    return;
+                } else if (line->buf[k - 1] != ' ') {
+                    // 2nd previous line is not all spaces
+                    break;
+                }
+            }
+        }
+        int n = (j - i) / 4;
+        if (line->buf[line->len - 2] == ':') {
+            n += 1;
+        }
+        while (n-- > 0) {
+            vstr_add_strn(line, "    ", 4);
+            mp_hal_stdout_tx_strn("    ", 4);
+            rl.cursor_pos += 4;
+        }
+    }
+}
+#endif
+
+void readline_note_newline(const char *prompt) {
+    rl.orig_line_len = rl.line->len;
+    rl.cursor_pos = rl.orig_line_len;
+    rl.prompt = prompt;
+    mp_hal_stdout_tx_str(prompt);
+    #if MICROPY_REPL_AUTO_INDENT
+    readline_auto_indent();
+    #endif
+}
+
+void readline_init(vstr_t *line, const char *prompt) {
+    rl.line = line;
+    rl.orig_line_len = line->len;
+    rl.escape_seq = ESEQ_NONE;
+    rl.escape_seq_buf[0] = 0;
+    rl.hist_cur = -1;
+    rl.cursor_pos = rl.orig_line_len;
+    rl.prompt = prompt;
+    mp_hal_stdout_tx_str(prompt);
+    #if MICROPY_REPL_AUTO_INDENT
+    readline_auto_indent();
+    #endif
+}
+
+int readline(vstr_t *line, const char *prompt) {
+    readline_init(line, prompt);
+    for (;;) {
+        int c = mp_hal_stdin_rx_chr();
+        int r = readline_process_char(c);
+        if (r >= 0) {
+            return r;
+        }
+    }
+}
+
+void readline_push_history(const char *line) {
+    if (line[0] != '\0'
+        && (MP_STATE_PORT(readline_hist)[0] == NULL
+            || strcmp(MP_STATE_PORT(readline_hist)[0], line) != 0)) {
+        // a line which is not empty and different from the last one
+        // so update the history
+        char *most_recent_hist = str_dup_maybe(line);
+        if (most_recent_hist != NULL) {
+            for (int i = READLINE_HIST_SIZE - 1; i > 0; i--) {
+                MP_STATE_PORT(readline_hist)[i] = MP_STATE_PORT(readline_hist)[i - 1];
+            }
+            MP_STATE_PORT(readline_hist)[0] = most_recent_hist;
+        }
+    }
+}
diff --git a/shared/readline/readline.h b/shared/readline/readline.h
new file mode 100644
index 000000000..a19e1209a
--- /dev/null
+++ b/shared/readline/readline.h
@@ -0,0 +1,49 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_MP_READLINE_READLINE_H
+#define MICROPY_INCLUDED_LIB_MP_READLINE_READLINE_H
+
+#define CHAR_CTRL_A (1)
+#define CHAR_CTRL_B (2)
+#define CHAR_CTRL_C (3)
+#define CHAR_CTRL_D (4)
+#define CHAR_CTRL_E (5)
+#define CHAR_CTRL_F (6)
+#define CHAR_CTRL_K (11)
+#define CHAR_CTRL_N (14)
+#define CHAR_CTRL_P (16)
+#define CHAR_CTRL_U (21)
+#define CHAR_CTRL_W (23)
+
+void readline_init0(void);
+int readline(vstr_t *line, const char *prompt);
+void readline_push_history(const char *line);
+
+void readline_init(vstr_t *line, const char *prompt);
+void readline_note_newline(const char *prompt);
+int readline_process_char(int c);
+
+#endif // MICROPY_INCLUDED_LIB_MP_READLINE_READLINE_H
diff --git a/shared/runtime/gchelper.h b/shared/runtime/gchelper.h
new file mode 100644
index 000000000..645ee837f
--- /dev/null
+++ b/shared/runtime/gchelper.h
@@ -0,0 +1,50 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_UTILS_GCHELPER_H
+#define MICROPY_INCLUDED_LIB_UTILS_GCHELPER_H
+
+#include <stdint.h>
+
+#if MICROPY_GCREGS_SETJMP
+#include <setjmp.h>
+typedef jmp_buf gc_helper_regs_t;
+#else
+
+#if defined(__x86_64__)
+typedef uintptr_t gc_helper_regs_t[6];
+#elif defined(__i386__)
+typedef uintptr_t gc_helper_regs_t[4];
+#elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__)
+typedef uintptr_t gc_helper_regs_t[10];
+#elif defined(__aarch64__)
+typedef uintptr_t gc_helper_regs_t[11]; // x19-x29
+#endif
+
+#endif
+
+void gc_helper_collect_regs_and_stack(void);
+
+#endif // MICROPY_INCLUDED_LIB_UTILS_GCHELPER_H
diff --git a/shared/runtime/gchelper_generic.c b/shared/runtime/gchelper_generic.c
new file mode 100644
index 000000000..3e7e33ab1
--- /dev/null
+++ b/shared/runtime/gchelper_generic.c
@@ -0,0 +1,183 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "py/mpstate.h"
+#include "py/gc.h"
+#include "lib/utils/gchelper.h"
+
+#if MICROPY_ENABLE_GC
+
+// Even if we have specific support for an architecture, it is
+// possible to force use of setjmp-based implementation.
+#if !MICROPY_GCREGS_SETJMP
+
+// We capture here callee-save registers, i.e. ones which may contain
+// interesting values held there by our callers. It doesn't make sense
+// to capture caller-saved registers, because they, well, put on the
+// stack already by the caller.
+#if defined(__x86_64__)
+
+STATIC void gc_helper_get_regs(gc_helper_regs_t arr) {
+    register long rbx asm ("rbx");
+    register long rbp asm ("rbp");
+    register long r12 asm ("r12");
+    register long r13 asm ("r13");
+    register long r14 asm ("r14");
+    register long r15 asm ("r15");
+    #ifdef __clang__
+    // TODO:
+    // This is dirty workaround for Clang. It tries to get around
+    // uncompliant (wrt to GCC) behavior of handling register variables.
+    // Application of this patch here is random, and done only to unbreak
+    // MacOS build. Better, cross-arch ways to deal with Clang issues should
+    // be found.
+    asm ("" : "=r" (rbx));
+    asm ("" : "=r" (rbp));
+    asm ("" : "=r" (r12));
+    asm ("" : "=r" (r13));
+    asm ("" : "=r" (r14));
+    asm ("" : "=r" (r15));
+    #endif
+    arr[0] = rbx;
+    arr[1] = rbp;
+    arr[2] = r12;
+    arr[3] = r13;
+    arr[4] = r14;
+    arr[5] = r15;
+}
+
+#elif defined(__i386__)
+
+STATIC void gc_helper_get_regs(gc_helper_regs_t arr) {
+    register long ebx asm ("ebx");
+    register long esi asm ("esi");
+    register long edi asm ("edi");
+    register long ebp asm ("ebp");
+    #ifdef __clang__
+    // TODO:
+    // This is dirty workaround for Clang. It tries to get around
+    // uncompliant (wrt to GCC) behavior of handling register variables.
+    // Application of this patch here is random, and done only to unbreak
+    // MacOS build. Better, cross-arch ways to deal with Clang issues should
+    // be found.
+    asm ("" : "=r" (ebx));
+    asm ("" : "=r" (esi));
+    asm ("" : "=r" (edi));
+    asm ("" : "=r" (ebp));
+    #endif
+    arr[0] = ebx;
+    arr[1] = esi;
+    arr[2] = edi;
+    arr[3] = ebp;
+}
+
+#elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__)
+
+// Fallback implementation, prefer gchelper_m0.s or gchelper_m3.s
+
+STATIC void gc_helper_get_regs(gc_helper_regs_t arr) {
+    register long r4 asm ("r4");
+    register long r5 asm ("r5");
+    register long r6 asm ("r6");
+    register long r7 asm ("r7");
+    register long r8 asm ("r8");
+    register long r9 asm ("r9");
+    register long r10 asm ("r10");
+    register long r11 asm ("r11");
+    register long r12 asm ("r12");
+    register long r13 asm ("r13");
+    arr[0] = r4;
+    arr[1] = r5;
+    arr[2] = r6;
+    arr[3] = r7;
+    arr[4] = r8;
+    arr[5] = r9;
+    arr[6] = r10;
+    arr[7] = r11;
+    arr[8] = r12;
+    arr[9] = r13;
+}
+
+#elif defined(__aarch64__)
+
+STATIC void gc_helper_get_regs(gc_helper_regs_t arr) {
+    const register long x19 asm ("x19");
+    const register long x20 asm ("x20");
+    const register long x21 asm ("x21");
+    const register long x22 asm ("x22");
+    const register long x23 asm ("x23");
+    const register long x24 asm ("x24");
+    const register long x25 asm ("x25");
+    const register long x26 asm ("x26");
+    const register long x27 asm ("x27");
+    const register long x28 asm ("x28");
+    const register long x29 asm ("x29");
+    arr[0] = x19;
+    arr[1] = x20;
+    arr[2] = x21;
+    arr[3] = x22;
+    arr[4] = x23;
+    arr[5] = x24;
+    arr[6] = x25;
+    arr[7] = x26;
+    arr[8] = x27;
+    arr[9] = x28;
+    arr[10] = x29;
+}
+
+#else
+
+#error "Architecture not supported for gc_helper_get_regs. Set MICROPY_GCREGS_SETJMP to use the fallback implementation."
+
+#endif
+
+#else // !MICROPY_GCREGS_SETJMP
+
+// Even if we have specific support for an architecture, it is
+// possible to force use of setjmp-based implementation.
+
+STATIC void gc_helper_get_regs(gc_helper_regs_t arr) {
+    setjmp(arr);
+}
+
+#endif // MICROPY_GCREGS_SETJMP
+
+// Explicitly mark this as noinline to make sure the regs variable
+// is effectively at the top of the stack: otherwise, in builds where
+// LTO is enabled and a lot of inlining takes place we risk a stack
+// layout where regs is lower on the stack than pointers which have
+// just been allocated but not yet marked, and get incorrectly sweeped.
+MP_NOINLINE void gc_helper_collect_regs_and_stack(void) {
+    gc_helper_regs_t regs;
+    gc_helper_get_regs(regs);
+    // GC stack (and regs because we captured them)
+    void **regs_ptr = (void **)(void *)&regs;
+    gc_collect_root(regs_ptr, ((uintptr_t)MP_STATE_THREAD(stack_top) - (uintptr_t)&regs) / sizeof(uintptr_t));
+}
+
+#endif // MICROPY_ENABLE_GC
diff --git a/shared/runtime/gchelper_m0.s b/shared/runtime/gchelper_m0.s
new file mode 100644
index 000000000..db0d9738d
--- /dev/null
+++ b/shared/runtime/gchelper_m0.s
@@ -0,0 +1,61 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+    .syntax unified
+    .cpu cortex-m0
+    .thumb
+
+    .section .text
+    .align 2
+
+    .global gc_helper_get_regs_and_sp
+    .type gc_helper_get_regs_and_sp, %function
+
+@ uint gc_helper_get_regs_and_sp(r0=uint regs[10])
+gc_helper_get_regs_and_sp:
+    @ store registers into given array
+    str    r4, [r0, #0]
+    str    r5, [r0, #4]
+    str    r6, [r0, #8]
+    str    r7, [r0, #12]
+    mov    r1, r8
+    str    r1, [r0, #16]
+    mov    r1, r9
+    str    r1, [r0, #20]
+    mov    r1, r10
+    str    r1, [r0, #24]
+    mov    r1, r11
+    str    r1, [r0, #28]
+    mov    r1, r12
+    str    r1, [r0, #32]
+    mov    r1, r13
+    str    r1, [r0, #36]
+
+    @ return the sp
+    mov    r0, sp
+    bx     lr
+
+    .size gc_helper_get_regs_and_sp, .-gc_helper_get_regs_and_sp
diff --git a/shared/runtime/gchelper_m3.s b/shared/runtime/gchelper_m3.s
new file mode 100644
index 000000000..5220fa088
--- /dev/null
+++ b/shared/runtime/gchelper_m3.s
@@ -0,0 +1,55 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+    .syntax unified
+    .cpu cortex-m3
+    .thumb
+
+    .section .text
+    .align  2
+
+    .global gc_helper_get_regs_and_sp
+    .type gc_helper_get_regs_and_sp, %function
+
+@ uint gc_helper_get_regs_and_sp(r0=uint regs[10])
+gc_helper_get_regs_and_sp:
+    @ store registers into given array
+    str     r4, [r0], #4
+    str     r5, [r0], #4
+    str     r6, [r0], #4
+    str     r7, [r0], #4
+    str     r8, [r0], #4
+    str     r9, [r0], #4
+    str     r10, [r0], #4
+    str     r11, [r0], #4
+    str     r12, [r0], #4
+    str     r13, [r0], #4
+
+    @ return the sp
+    mov     r0, sp
+    bx      lr
+
+    .size gc_helper_get_regs_and_sp, .-gc_helper_get_regs_and_sp
diff --git a/shared/runtime/gchelper_native.c b/shared/runtime/gchelper_native.c
new file mode 100644
index 000000000..6bf386b51
--- /dev/null
+++ b/shared/runtime/gchelper_native.c
@@ -0,0 +1,47 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "py/mpstate.h"
+#include "py/gc.h"
+#include "lib/utils/gchelper.h"
+
+#if MICROPY_ENABLE_GC
+
+// provided by gchelper_*.s
+uintptr_t gc_helper_get_regs_and_sp(uintptr_t *regs);
+
+MP_NOINLINE void gc_helper_collect_regs_and_stack(void) {
+    // get the registers and the sp
+    gc_helper_regs_t regs;
+    uintptr_t sp = gc_helper_get_regs_and_sp(regs);
+
+    // trace the stack, including the registers (since they live on the stack in this function)
+    gc_collect_root((void **)sp, ((uint32_t)MP_STATE_THREAD(stack_top) - sp) / sizeof(uint32_t));
+}
+
+#endif
diff --git a/shared/runtime/interrupt_char.c b/shared/runtime/interrupt_char.c
new file mode 100644
index 000000000..7014ae6a8
--- /dev/null
+++ b/shared/runtime/interrupt_char.c
@@ -0,0 +1,38 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2016 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/obj.h"
+#include "py/mpstate.h"
+
+#if MICROPY_KBD_EXCEPTION
+
+int mp_interrupt_char = -1;
+
+void mp_hal_set_interrupt_char(int c) {
+    mp_interrupt_char = c;
+}
+
+#endif
diff --git a/shared/runtime/interrupt_char.h b/shared/runtime/interrupt_char.h
new file mode 100644
index 000000000..cb086ead9
--- /dev/null
+++ b/shared/runtime/interrupt_char.h
@@ -0,0 +1,32 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2016 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_UTILS_INTERRUPT_CHAR_H
+#define MICROPY_INCLUDED_LIB_UTILS_INTERRUPT_CHAR_H
+
+extern int mp_interrupt_char;
+void mp_hal_set_interrupt_char(int c);
+
+#endif // MICROPY_INCLUDED_LIB_UTILS_INTERRUPT_CHAR_H
diff --git a/shared/runtime/mpirq.c b/shared/runtime/mpirq.c
new file mode 100644
index 000000000..02139f24d
--- /dev/null
+++ b/shared/runtime/mpirq.c
@@ -0,0 +1,135 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Daniel Campora
+ *               2018 Tobias Badertscher
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "py/runtime.h"
+#include "py/gc.h"
+#include "lib/utils/mpirq.h"
+
+#if MICROPY_ENABLE_SCHEDULER
+
+/******************************************************************************
+ DECLARE PUBLIC DATA
+ ******************************************************************************/
+
+const mp_arg_t mp_irq_init_args[] = {
+    { MP_QSTR_handler, MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+    { MP_QSTR_trigger, MP_ARG_INT, {.u_int = 0} },
+    { MP_QSTR_hard, MP_ARG_BOOL, {.u_bool = false} },
+};
+
+/******************************************************************************
+ DECLARE PRIVATE DATA
+ ******************************************************************************/
+
+/******************************************************************************
+ DEFINE PUBLIC FUNCTIONS
+ ******************************************************************************/
+
+mp_irq_obj_t *mp_irq_new(const mp_irq_methods_t *methods, mp_obj_t parent) {
+    mp_irq_obj_t *self = m_new0(mp_irq_obj_t, 1);
+    mp_irq_init(self, methods, parent);
+    return self;
+}
+
+void mp_irq_init(mp_irq_obj_t *self, const mp_irq_methods_t *methods, mp_obj_t parent) {
+    self->base.type = &mp_irq_type;
+    self->methods = (mp_irq_methods_t *)methods;
+    self->parent = parent;
+    self->handler = mp_const_none;
+    self->ishard = false;
+}
+
+void mp_irq_handler(mp_irq_obj_t *self) {
+    if (self->handler != mp_const_none) {
+        if (self->ishard) {
+            // When executing code within a handler we must lock the scheduler to
+            // prevent any scheduled callbacks from running, and lock the GC to
+            // prevent any memory allocations.
+            mp_sched_lock();
+            gc_lock();
+            nlr_buf_t nlr;
+            if (nlr_push(&nlr) == 0) {
+                mp_call_function_1(self->handler, self->parent);
+                nlr_pop();
+            } else {
+                // Uncaught exception; disable the callback so that it doesn't run again
+                self->methods->trigger(self->parent, 0);
+                self->handler = mp_const_none;
+                printf("Uncaught exception in IRQ callback handler\n");
+                mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+            }
+            gc_unlock();
+            mp_sched_unlock();
+        } else {
+            // Schedule call to user function
+            mp_sched_schedule(self->handler, self->parent);
+        }
+    }
+}
+
+/******************************************************************************/
+// MicroPython bindings
+
+STATIC mp_obj_t mp_irq_flags(mp_obj_t self_in) {
+    mp_irq_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    return mp_obj_new_int(self->methods->info(self->parent, MP_IRQ_INFO_FLAGS));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_irq_flags_obj, mp_irq_flags);
+
+STATIC mp_obj_t mp_irq_trigger(size_t n_args, const mp_obj_t *args) {
+    mp_irq_obj_t *self = MP_OBJ_TO_PTR(args[0]);
+    mp_obj_t ret_obj = mp_obj_new_int(self->methods->info(self->parent, MP_IRQ_INFO_TRIGGERS));
+    if (n_args == 2) {
+        // Set trigger
+        self->methods->trigger(self->parent, mp_obj_get_int(args[1]));
+    }
+    return ret_obj;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_irq_trigger_obj, 1, 2, mp_irq_trigger);
+
+STATIC mp_obj_t mp_irq_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    mp_arg_check_num(n_args, n_kw, 0, 0, false);
+    mp_irq_handler(MP_OBJ_TO_PTR(self_in));
+    return mp_const_none;
+}
+
+STATIC const mp_rom_map_elem_t mp_irq_locals_dict_table[] = {
+    { MP_ROM_QSTR(MP_QSTR_flags),               MP_ROM_PTR(&mp_irq_flags_obj) },
+    { MP_ROM_QSTR(MP_QSTR_trigger),             MP_ROM_PTR(&mp_irq_trigger_obj) },
+};
+STATIC MP_DEFINE_CONST_DICT(mp_irq_locals_dict, mp_irq_locals_dict_table);
+
+const mp_obj_type_t mp_irq_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_irq,
+    .call = mp_irq_call,
+    .locals_dict = (mp_obj_dict_t *)&mp_irq_locals_dict,
+};
+
+#endif // MICROPY_ENABLE_SCHEDULER
diff --git a/shared/runtime/mpirq.h b/shared/runtime/mpirq.h
new file mode 100644
index 000000000..dd423c010
--- /dev/null
+++ b/shared/runtime/mpirq.h
@@ -0,0 +1,82 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Daniel Campora
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_UTILS_MPIRQ_H
+#define MICROPY_INCLUDED_LIB_UTILS_MPIRQ_H
+
+#include "py/runtime.h"
+
+/******************************************************************************
+ DEFINE CONSTANTS
+ ******************************************************************************/
+
+enum {
+    MP_IRQ_ARG_INIT_handler = 0,
+    MP_IRQ_ARG_INIT_trigger,
+    MP_IRQ_ARG_INIT_hard,
+    MP_IRQ_ARG_INIT_NUM_ARGS,
+};
+
+/******************************************************************************
+ DEFINE TYPES
+ ******************************************************************************/
+
+typedef mp_uint_t (*mp_irq_trigger_fun_t)(mp_obj_t self, mp_uint_t trigger);
+typedef mp_uint_t (*mp_irq_info_fun_t)(mp_obj_t self, mp_uint_t info_type);
+
+enum {
+    MP_IRQ_INFO_FLAGS,
+    MP_IRQ_INFO_TRIGGERS,
+};
+
+typedef struct _mp_irq_methods_t {
+    mp_irq_trigger_fun_t trigger;
+    mp_irq_info_fun_t info;
+} mp_irq_methods_t;
+
+typedef struct _mp_irq_obj_t {
+    mp_obj_base_t base;
+    mp_irq_methods_t *methods;
+    mp_obj_t parent;
+    mp_obj_t handler;
+    bool ishard;
+} mp_irq_obj_t;
+
+/******************************************************************************
+ DECLARE EXPORTED DATA
+ ******************************************************************************/
+
+extern const mp_arg_t mp_irq_init_args[];
+extern const mp_obj_type_t mp_irq_type;
+
+/******************************************************************************
+ DECLARE PUBLIC FUNCTIONS
+ ******************************************************************************/
+
+mp_irq_obj_t *mp_irq_new(const mp_irq_methods_t *methods, mp_obj_t parent);
+void mp_irq_init(mp_irq_obj_t *self, const mp_irq_methods_t *methods, mp_obj_t parent);
+void mp_irq_handler(mp_irq_obj_t *self);
+
+#endif // MICROPY_INCLUDED_LIB_UTILS_MPIRQ_H
diff --git a/shared/runtime/pyexec.c b/shared/runtime/pyexec.c
new file mode 100644
index 000000000..4446b36b6
--- /dev/null
+++ b/shared/runtime/pyexec.c
@@ -0,0 +1,716 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "py/compile.h"
+#include "py/runtime.h"
+#include "py/repl.h"
+#include "py/gc.h"
+#include "py/frozenmod.h"
+#include "py/mphal.h"
+#if MICROPY_HW_ENABLE_USB
+#include "irq.h"
+#include "usb.h"
+#endif
+#include "lib/mp-readline/readline.h"
+#include "lib/utils/pyexec.h"
+#include "genhdr/mpversion.h"
+
+pyexec_mode_kind_t pyexec_mode_kind = PYEXEC_MODE_FRIENDLY_REPL;
+int pyexec_system_exit = 0;
+
+#if MICROPY_REPL_INFO
+STATIC bool repl_display_debugging_info = 0;
+#endif
+
+#define EXEC_FLAG_PRINT_EOF (1)
+#define EXEC_FLAG_ALLOW_DEBUGGING (2)
+#define EXEC_FLAG_IS_REPL (4)
+#define EXEC_FLAG_SOURCE_IS_RAW_CODE (8)
+#define EXEC_FLAG_SOURCE_IS_VSTR (16)
+#define EXEC_FLAG_SOURCE_IS_FILENAME (32)
+#define EXEC_FLAG_SOURCE_IS_READER (64)
+
+// parses, compiles and executes the code in the lexer
+// frees the lexer before returning
+// EXEC_FLAG_PRINT_EOF prints 2 EOF chars: 1 after normal output, 1 after exception output
+// EXEC_FLAG_ALLOW_DEBUGGING allows debugging info to be printed after executing the code
+// EXEC_FLAG_IS_REPL is used for REPL inputs (flag passed on to mp_compile)
+STATIC int parse_compile_execute(const void *source, mp_parse_input_kind_t input_kind, int exec_flags) {
+    int ret = 0;
+    #if MICROPY_REPL_INFO
+    uint32_t start = 0;
+    #endif
+
+    #ifdef MICROPY_BOARD_BEFORE_PYTHON_EXEC
+    MICROPY_BOARD_BEFORE_PYTHON_EXEC(input_kind, exec_flags);
+    #endif
+
+    // by default a SystemExit exception returns 0
+    pyexec_system_exit = 0;
+
+    nlr_buf_t nlr;
+    nlr.ret_val = NULL;
+    if (nlr_push(&nlr) == 0) {
+        mp_obj_t module_fun;
+        #if MICROPY_MODULE_FROZEN_MPY
+        if (exec_flags & EXEC_FLAG_SOURCE_IS_RAW_CODE) {
+            // source is a raw_code object, create the function
+            module_fun = mp_make_function_from_raw_code(source, MP_OBJ_NULL, MP_OBJ_NULL);
+        } else
+        #endif
+        {
+            #if MICROPY_ENABLE_COMPILER
+            mp_lexer_t *lex;
+            if (exec_flags & EXEC_FLAG_SOURCE_IS_VSTR) {
+                const vstr_t *vstr = source;
+                lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, vstr->buf, vstr->len, 0);
+            } else if (exec_flags & EXEC_FLAG_SOURCE_IS_READER) {
+                lex = mp_lexer_new(MP_QSTR__lt_stdin_gt_, *(mp_reader_t *)source);
+            } else if (exec_flags & EXEC_FLAG_SOURCE_IS_FILENAME) {
+                lex = mp_lexer_new_from_file(source);
+            } else {
+                lex = (mp_lexer_t *)source;
+            }
+            // source is a lexer, parse and compile the script
+            qstr source_name = lex->source_name;
+            mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
+            module_fun = mp_compile(&parse_tree, source_name, exec_flags & EXEC_FLAG_IS_REPL);
+            #else
+            mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT("script compilation not supported"));
+            #endif
+        }
+
+        // execute code
+        mp_hal_set_interrupt_char(CHAR_CTRL_C); // allow ctrl-C to interrupt us
+        #if MICROPY_REPL_INFO
+        start = mp_hal_ticks_ms();
+        #endif
+        mp_call_function_0(module_fun);
+        mp_hal_set_interrupt_char(-1); // disable interrupt
+        mp_handle_pending(true); // handle any pending exceptions (and any callbacks)
+        nlr_pop();
+        ret = 1;
+        if (exec_flags & EXEC_FLAG_PRINT_EOF) {
+            mp_hal_stdout_tx_strn("\x04", 1);
+        }
+    } else {
+        // uncaught exception
+        mp_hal_set_interrupt_char(-1); // disable interrupt
+        mp_handle_pending(false); // clear any pending exceptions (and run any callbacks)
+
+        if (exec_flags & EXEC_FLAG_SOURCE_IS_READER) {
+            const mp_reader_t *reader = source;
+            reader->close(reader->data);
+        }
+
+        // print EOF after normal output
+        if (exec_flags & EXEC_FLAG_PRINT_EOF) {
+            mp_hal_stdout_tx_strn("\x04", 1);
+        }
+        // check for SystemExit
+        if (mp_obj_is_subclass_fast(MP_OBJ_FROM_PTR(((mp_obj_base_t *)nlr.ret_val)->type), MP_OBJ_FROM_PTR(&mp_type_SystemExit))) {
+            // at the moment, the value of SystemExit is unused
+            ret = pyexec_system_exit;
+        } else {
+            mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+            ret = 0;
+        }
+    }
+
+    #if MICROPY_REPL_INFO
+    // display debugging info if wanted
+    if ((exec_flags & EXEC_FLAG_ALLOW_DEBUGGING) && repl_display_debugging_info) {
+        mp_uint_t ticks = mp_hal_ticks_ms() - start; // TODO implement a function that does this properly
+        printf("took " UINT_FMT " ms\n", ticks);
+        // qstr info
+        {
+            size_t n_pool, n_qstr, n_str_data_bytes, n_total_bytes;
+            qstr_pool_info(&n_pool, &n_qstr, &n_str_data_bytes, &n_total_bytes);
+            printf("qstr:\n  n_pool=%u\n  n_qstr=%u\n  "
+                "n_str_data_bytes=%u\n  n_total_bytes=%u\n",
+                (unsigned)n_pool, (unsigned)n_qstr, (unsigned)n_str_data_bytes, (unsigned)n_total_bytes);
+        }
+
+        #if MICROPY_ENABLE_GC
+        // run collection and print GC info
+        gc_collect();
+        gc_dump_info();
+        #endif
+    }
+    #endif
+
+    if (exec_flags & EXEC_FLAG_PRINT_EOF) {
+        mp_hal_stdout_tx_strn("\x04", 1);
+    }
+
+    #ifdef MICROPY_BOARD_AFTER_PYTHON_EXEC
+    MICROPY_BOARD_AFTER_PYTHON_EXEC(input_kind, exec_flags, nlr.ret_val, &ret);
+    #endif
+
+    return ret;
+}
+
+#if MICROPY_ENABLE_COMPILER
+
+// This can be configured by a port (and even configured to a function to be
+// computed dynamically) to indicate the maximum number of bytes that can be
+// held in the stdin buffer.
+#ifndef MICROPY_REPL_STDIN_BUFFER_MAX
+#define MICROPY_REPL_STDIN_BUFFER_MAX (256)
+#endif
+
+typedef struct _mp_reader_stdin_t {
+    bool eof;
+    uint16_t window_max;
+    uint16_t window_remain;
+} mp_reader_stdin_t;
+
+STATIC mp_uint_t mp_reader_stdin_readbyte(void *data) {
+    mp_reader_stdin_t *reader = (mp_reader_stdin_t *)data;
+
+    if (reader->eof) {
+        return MP_READER_EOF;
+    }
+
+    int c = mp_hal_stdin_rx_chr();
+
+    if (c == CHAR_CTRL_C || c == CHAR_CTRL_D) {
+        reader->eof = true;
+        mp_hal_stdout_tx_strn("\x04", 1); // indicate end to host
+        if (c == CHAR_CTRL_C) {
+            #if MICROPY_KBD_EXCEPTION
+            MP_STATE_VM(mp_kbd_exception).traceback_data = NULL;
+            nlr_raise(MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception)));
+            #else
+            mp_raise_type(&mp_type_KeyboardInterrupt);
+            #endif
+        } else {
+            return MP_READER_EOF;
+        }
+    }
+
+    if (--reader->window_remain == 0) {
+        mp_hal_stdout_tx_strn("\x01", 1); // indicate window available to host
+        reader->window_remain = reader->window_max;
+    }
+
+    return c;
+}
+
+STATIC void mp_reader_stdin_close(void *data) {
+    mp_reader_stdin_t *reader = (mp_reader_stdin_t *)data;
+    if (!reader->eof) {
+        reader->eof = true;
+        mp_hal_stdout_tx_strn("\x04", 1); // indicate end to host
+        for (;;) {
+            int c = mp_hal_stdin_rx_chr();
+            if (c == CHAR_CTRL_C || c == CHAR_CTRL_D) {
+                break;
+            }
+        }
+    }
+}
+
+STATIC void mp_reader_new_stdin(mp_reader_t *reader, mp_reader_stdin_t *reader_stdin, uint16_t buf_max) {
+    // Make flow-control window half the buffer size, and indicate to the host that 2x windows are
+    // free (sending the window size implicitly indicates that a window is free, and then the 0x01
+    // indicates that another window is free).
+    size_t window = buf_max / 2;
+    char reply[3] = { window & 0xff, window >> 8, 0x01 };
+    mp_hal_stdout_tx_strn(reply, sizeof(reply));
+
+    reader_stdin->eof = false;
+    reader_stdin->window_max = window;
+    reader_stdin->window_remain = window;
+    reader->data = reader_stdin;
+    reader->readbyte = mp_reader_stdin_readbyte;
+    reader->close = mp_reader_stdin_close;
+}
+
+STATIC int do_reader_stdin(int c) {
+    if (c != 'A') {
+        // Unsupported command.
+        mp_hal_stdout_tx_strn("R\x00", 2);
+        return 0;
+    }
+
+    // Indicate reception of command.
+    mp_hal_stdout_tx_strn("R\x01", 2);
+
+    mp_reader_t reader;
+    mp_reader_stdin_t reader_stdin;
+    mp_reader_new_stdin(&reader, &reader_stdin, MICROPY_REPL_STDIN_BUFFER_MAX);
+    int exec_flags = EXEC_FLAG_PRINT_EOF | EXEC_FLAG_SOURCE_IS_READER;
+    return parse_compile_execute(&reader, MP_PARSE_FILE_INPUT, exec_flags);
+}
+
+#if MICROPY_REPL_EVENT_DRIVEN
+
+typedef struct _repl_t {
+    // This structure originally also held current REPL line,
+    // but it was moved to MP_STATE_VM(repl_line) as containing
+    // root pointer. Still keep structure in case more state
+    // will be added later.
+    // vstr_t line;
+    bool cont_line;
+    bool paste_mode;
+} repl_t;
+
+repl_t repl;
+
+STATIC int pyexec_raw_repl_process_char(int c);
+STATIC int pyexec_friendly_repl_process_char(int c);
+
+void pyexec_event_repl_init(void) {
+    MP_STATE_VM(repl_line) = vstr_new(32);
+    repl.cont_line = false;
+    repl.paste_mode = false;
+    // no prompt before printing friendly REPL banner or entering raw REPL
+    readline_init(MP_STATE_VM(repl_line), "");
+    if (pyexec_mode_kind == PYEXEC_MODE_RAW_REPL) {
+        pyexec_raw_repl_process_char(CHAR_CTRL_A);
+    } else {
+        pyexec_friendly_repl_process_char(CHAR_CTRL_B);
+    }
+}
+
+STATIC int pyexec_raw_repl_process_char(int c) {
+    if (c == CHAR_CTRL_A) {
+        // reset raw REPL
+        if (vstr_len(MP_STATE_VM(repl_line)) == 2 && vstr_str(MP_STATE_VM(repl_line))[0] == CHAR_CTRL_E) {
+            int ret = do_reader_stdin(vstr_str(MP_STATE_VM(repl_line))[1]);
+            if (ret & PYEXEC_FORCED_EXIT) {
+                return ret;
+            }
+            goto reset;
+        }
+        mp_hal_stdout_tx_str("raw REPL; CTRL-B to exit\r\n");
+        goto reset;
+    } else if (c == CHAR_CTRL_B) {
+        // change to friendly REPL
+        pyexec_mode_kind = PYEXEC_MODE_FRIENDLY_REPL;
+        vstr_reset(MP_STATE_VM(repl_line));
+        repl.cont_line = false;
+        repl.paste_mode = false;
+        pyexec_friendly_repl_process_char(CHAR_CTRL_B);
+        return 0;
+    } else if (c == CHAR_CTRL_C) {
+        // clear line
+        vstr_reset(MP_STATE_VM(repl_line));
+        return 0;
+    } else if (c == CHAR_CTRL_D) {
+        // input finished
+    } else {
+        // let through any other raw 8-bit value
+        vstr_add_byte(MP_STATE_VM(repl_line), c);
+        return 0;
+    }
+
+    // indicate reception of command
+    mp_hal_stdout_tx_str("OK");
+
+    if (MP_STATE_VM(repl_line)->len == 0) {
+        // exit for a soft reset
+        mp_hal_stdout_tx_str("\r\n");
+        vstr_clear(MP_STATE_VM(repl_line));
+        return PYEXEC_FORCED_EXIT;
+    }
+
+    int ret = parse_compile_execute(MP_STATE_VM(repl_line), MP_PARSE_FILE_INPUT, EXEC_FLAG_PRINT_EOF | EXEC_FLAG_SOURCE_IS_VSTR);
+    if (ret & PYEXEC_FORCED_EXIT) {
+        return ret;
+    }
+
+reset:
+    vstr_reset(MP_STATE_VM(repl_line));
+    mp_hal_stdout_tx_str(">");
+
+    return 0;
+}
+
+STATIC int pyexec_friendly_repl_process_char(int c) {
+    if (repl.paste_mode) {
+        if (c == CHAR_CTRL_C) {
+            // cancel everything
+            mp_hal_stdout_tx_str("\r\n");
+            goto input_restart;
+        } else if (c == CHAR_CTRL_D) {
+            // end of input
+            mp_hal_stdout_tx_str("\r\n");
+            int ret = parse_compile_execute(MP_STATE_VM(repl_line), MP_PARSE_FILE_INPUT, EXEC_FLAG_ALLOW_DEBUGGING | EXEC_FLAG_IS_REPL | EXEC_FLAG_SOURCE_IS_VSTR);
+            if (ret & PYEXEC_FORCED_EXIT) {
+                return ret;
+            }
+            goto input_restart;
+        } else {
+            // add char to buffer and echo
+            vstr_add_byte(MP_STATE_VM(repl_line), c);
+            if (c == '\r') {
+                mp_hal_stdout_tx_str("\r\n=== ");
+            } else {
+                char buf[1] = {c};
+                mp_hal_stdout_tx_strn(buf, 1);
+            }
+            return 0;
+        }
+    }
+
+    int ret = readline_process_char(c);
+
+    if (!repl.cont_line) {
+
+        if (ret == CHAR_CTRL_A) {
+            // change to raw REPL
+            pyexec_mode_kind = PYEXEC_MODE_RAW_REPL;
+            mp_hal_stdout_tx_str("\r\n");
+            pyexec_raw_repl_process_char(CHAR_CTRL_A);
+            return 0;
+        } else if (ret == CHAR_CTRL_B) {
+            // reset friendly REPL
+            mp_hal_stdout_tx_str("\r\n");
+            mp_hal_stdout_tx_str("MicroPython " MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE "; " MICROPY_HW_BOARD_NAME " with " MICROPY_HW_MCU_NAME "\r\n");
+            #if MICROPY_PY_BUILTINS_HELP
+            mp_hal_stdout_tx_str("Type \"help()\" for more information.\r\n");
+            #endif
+            goto input_restart;
+        } else if (ret == CHAR_CTRL_C) {
+            // break
+            mp_hal_stdout_tx_str("\r\n");
+            goto input_restart;
+        } else if (ret == CHAR_CTRL_D) {
+            // exit for a soft reset
+            mp_hal_stdout_tx_str("\r\n");
+            vstr_clear(MP_STATE_VM(repl_line));
+            return PYEXEC_FORCED_EXIT;
+        } else if (ret == CHAR_CTRL_E) {
+            // paste mode
+            mp_hal_stdout_tx_str("\r\npaste mode; Ctrl-C to cancel, Ctrl-D to finish\r\n=== ");
+            vstr_reset(MP_STATE_VM(repl_line));
+            repl.paste_mode = true;
+            return 0;
+        }
+
+        if (ret < 0) {
+            return 0;
+        }
+
+        if (!mp_repl_continue_with_input(vstr_null_terminated_str(MP_STATE_VM(repl_line)))) {
+            goto exec;
+        }
+
+        vstr_add_byte(MP_STATE_VM(repl_line), '\n');
+        repl.cont_line = true;
+        readline_note_newline("... ");
+        return 0;
+
+    } else {
+
+        if (ret == CHAR_CTRL_C) {
+            // cancel everything
+            mp_hal_stdout_tx_str("\r\n");
+            repl.cont_line = false;
+            goto input_restart;
+        } else if (ret == CHAR_CTRL_D) {
+            // stop entering compound statement
+            goto exec;
+        }
+
+        if (ret < 0) {
+            return 0;
+        }
+
+        if (mp_repl_continue_with_input(vstr_null_terminated_str(MP_STATE_VM(repl_line)))) {
+            vstr_add_byte(MP_STATE_VM(repl_line), '\n');
+            readline_note_newline("... ");
+            return 0;
+        }
+
+    exec:;
+        int ret = parse_compile_execute(MP_STATE_VM(repl_line), MP_PARSE_SINGLE_INPUT, EXEC_FLAG_ALLOW_DEBUGGING | EXEC_FLAG_IS_REPL | EXEC_FLAG_SOURCE_IS_VSTR);
+        if (ret & PYEXEC_FORCED_EXIT) {
+            return ret;
+        }
+
+    input_restart:
+        vstr_reset(MP_STATE_VM(repl_line));
+        repl.cont_line = false;
+        repl.paste_mode = false;
+        readline_init(MP_STATE_VM(repl_line), ">>> ");
+        return 0;
+    }
+}
+
+uint8_t pyexec_repl_active;
+int pyexec_event_repl_process_char(int c) {
+    pyexec_repl_active = 1;
+    int res;
+    if (pyexec_mode_kind == PYEXEC_MODE_RAW_REPL) {
+        res = pyexec_raw_repl_process_char(c);
+    } else {
+        res = pyexec_friendly_repl_process_char(c);
+    }
+    pyexec_repl_active = 0;
+    return res;
+}
+
+#else // MICROPY_REPL_EVENT_DRIVEN
+
+int pyexec_raw_repl(void) {
+    vstr_t line;
+    vstr_init(&line, 32);
+
+raw_repl_reset:
+    mp_hal_stdout_tx_str("raw REPL; CTRL-B to exit\r\n");
+
+    for (;;) {
+        vstr_reset(&line);
+        mp_hal_stdout_tx_str(">");
+        for (;;) {
+            int c = mp_hal_stdin_rx_chr();
+            if (c == CHAR_CTRL_A) {
+                // reset raw REPL
+                if (vstr_len(&line) == 2 && vstr_str(&line)[0] == CHAR_CTRL_E) {
+                    int ret = do_reader_stdin(vstr_str(&line)[1]);
+                    if (ret & PYEXEC_FORCED_EXIT) {
+                        return ret;
+                    }
+                    vstr_reset(&line);
+                    mp_hal_stdout_tx_str(">");
+                    continue;
+                }
+                goto raw_repl_reset;
+            } else if (c == CHAR_CTRL_B) {
+                // change to friendly REPL
+                mp_hal_stdout_tx_str("\r\n");
+                vstr_clear(&line);
+                pyexec_mode_kind = PYEXEC_MODE_FRIENDLY_REPL;
+                return 0;
+            } else if (c == CHAR_CTRL_C) {
+                // clear line
+                vstr_reset(&line);
+            } else if (c == CHAR_CTRL_D) {
+                // input finished
+                break;
+            } else {
+                // let through any other raw 8-bit value
+                vstr_add_byte(&line, c);
+            }
+        }
+
+        // indicate reception of command
+        mp_hal_stdout_tx_str("OK");
+
+        if (line.len == 0) {
+            // exit for a soft reset
+            mp_hal_stdout_tx_str("\r\n");
+            vstr_clear(&line);
+            return PYEXEC_FORCED_EXIT;
+        }
+
+        int ret = parse_compile_execute(&line, MP_PARSE_FILE_INPUT, EXEC_FLAG_PRINT_EOF | EXEC_FLAG_SOURCE_IS_VSTR);
+        if (ret & PYEXEC_FORCED_EXIT) {
+            return ret;
+        }
+    }
+}
+
+int pyexec_friendly_repl(void) {
+    vstr_t line;
+    vstr_init(&line, 32);
+
+friendly_repl_reset:
+    mp_hal_stdout_tx_str("MicroPython " MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE "; " MICROPY_HW_BOARD_NAME " with " MICROPY_HW_MCU_NAME "\r\n");
+    #if MICROPY_PY_BUILTINS_HELP
+    mp_hal_stdout_tx_str("Type \"help()\" for more information.\r\n");
+    #endif
+
+    // to test ctrl-C
+    /*
+    {
+        uint32_t x[4] = {0x424242, 0xdeaddead, 0x242424, 0xdeadbeef};
+        for (;;) {
+            nlr_buf_t nlr;
+            printf("pyexec_repl: %p\n", x);
+            mp_hal_set_interrupt_char(CHAR_CTRL_C);
+            if (nlr_push(&nlr) == 0) {
+                for (;;) {
+                }
+            } else {
+                printf("break\n");
+            }
+        }
+    }
+    */
+
+    for (;;) {
+    input_restart:
+
+        #if MICROPY_HW_ENABLE_USB
+        if (usb_vcp_is_enabled()) {
+            // If the user gets to here and interrupts are disabled then
+            // they'll never see the prompt, traceback etc. The USB REPL needs
+            // interrupts to be enabled or no transfers occur. So we try to
+            // do the user a favor and reenable interrupts.
+            if (query_irq() == IRQ_STATE_DISABLED) {
+                enable_irq(IRQ_STATE_ENABLED);
+                mp_hal_stdout_tx_str("MPY: enabling IRQs\r\n");
+            }
+        }
+        #endif
+
+        // If the GC is locked at this point there is no way out except a reset,
+        // so force the GC to be unlocked to help the user debug what went wrong.
+        if (MP_STATE_THREAD(gc_lock_depth) != 0) {
+            MP_STATE_THREAD(gc_lock_depth) = 0;
+        }
+
+        vstr_reset(&line);
+        int ret = readline(&line, ">>> ");
+        mp_parse_input_kind_t parse_input_kind = MP_PARSE_SINGLE_INPUT;
+
+        if (ret == CHAR_CTRL_A) {
+            // change to raw REPL
+            mp_hal_stdout_tx_str("\r\n");
+            vstr_clear(&line);
+            pyexec_mode_kind = PYEXEC_MODE_RAW_REPL;
+            return 0;
+        } else if (ret == CHAR_CTRL_B) {
+            // reset friendly REPL
+            mp_hal_stdout_tx_str("\r\n");
+            goto friendly_repl_reset;
+        } else if (ret == CHAR_CTRL_C) {
+            // break
+            mp_hal_stdout_tx_str("\r\n");
+            continue;
+        } else if (ret == CHAR_CTRL_D) {
+            // exit for a soft reset
+            mp_hal_stdout_tx_str("\r\n");
+            vstr_clear(&line);
+            return PYEXEC_FORCED_EXIT;
+        } else if (ret == CHAR_CTRL_E) {
+            // paste mode
+            mp_hal_stdout_tx_str("\r\npaste mode; Ctrl-C to cancel, Ctrl-D to finish\r\n=== ");
+            vstr_reset(&line);
+            for (;;) {
+                char c = mp_hal_stdin_rx_chr();
+                if (c == CHAR_CTRL_C) {
+                    // cancel everything
+                    mp_hal_stdout_tx_str("\r\n");
+                    goto input_restart;
+                } else if (c == CHAR_CTRL_D) {
+                    // end of input
+                    mp_hal_stdout_tx_str("\r\n");
+                    break;
+                } else {
+                    // add char to buffer and echo
+                    vstr_add_byte(&line, c);
+                    if (c == '\r') {
+                        mp_hal_stdout_tx_str("\r\n=== ");
+                    } else {
+                        mp_hal_stdout_tx_strn(&c, 1);
+                    }
+                }
+            }
+            parse_input_kind = MP_PARSE_FILE_INPUT;
+        } else if (vstr_len(&line) == 0) {
+            continue;
+        } else {
+            // got a line with non-zero length, see if it needs continuing
+            while (mp_repl_continue_with_input(vstr_null_terminated_str(&line))) {
+                vstr_add_byte(&line, '\n');
+                ret = readline(&line, "... ");
+                if (ret == CHAR_CTRL_C) {
+                    // cancel everything
+                    mp_hal_stdout_tx_str("\r\n");
+                    goto input_restart;
+                } else if (ret == CHAR_CTRL_D) {
+                    // stop entering compound statement
+                    break;
+                }
+            }
+        }
+
+        ret = parse_compile_execute(&line, parse_input_kind, EXEC_FLAG_ALLOW_DEBUGGING | EXEC_FLAG_IS_REPL | EXEC_FLAG_SOURCE_IS_VSTR);
+        if (ret & PYEXEC_FORCED_EXIT) {
+            return ret;
+        }
+    }
+}
+
+#endif // MICROPY_REPL_EVENT_DRIVEN
+#endif // MICROPY_ENABLE_COMPILER
+
+int pyexec_file(const char *filename) {
+    return parse_compile_execute(filename, MP_PARSE_FILE_INPUT, EXEC_FLAG_SOURCE_IS_FILENAME);
+}
+
+int pyexec_file_if_exists(const char *filename) {
+    #if MICROPY_MODULE_FROZEN
+    if (mp_frozen_stat(filename) == MP_IMPORT_STAT_FILE) {
+        return pyexec_frozen_module(filename);
+    }
+    #endif
+    if (mp_import_stat(filename) != MP_IMPORT_STAT_FILE) {
+        return 1; // success (no file is the same as an empty file executing without fail)
+    }
+    return pyexec_file(filename);
+}
+
+#if MICROPY_MODULE_FROZEN
+int pyexec_frozen_module(const char *name) {
+    void *frozen_data;
+    int frozen_type = mp_find_frozen_module(name, strlen(name), &frozen_data);
+
+    switch (frozen_type) {
+        #if MICROPY_MODULE_FROZEN_STR
+        case MP_FROZEN_STR:
+            return parse_compile_execute(frozen_data, MP_PARSE_FILE_INPUT, 0);
+        #endif
+
+        #if MICROPY_MODULE_FROZEN_MPY
+        case MP_FROZEN_MPY:
+            return parse_compile_execute(frozen_data, MP_PARSE_FILE_INPUT, EXEC_FLAG_SOURCE_IS_RAW_CODE);
+        #endif
+
+        default:
+            printf("could not find module '%s'\n", name);
+            return false;
+    }
+}
+#endif
+
+#if MICROPY_REPL_INFO
+mp_obj_t pyb_set_repl_info(mp_obj_t o_value) {
+    repl_display_debugging_info = mp_obj_get_int(o_value);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(pyb_set_repl_info_obj, pyb_set_repl_info);
+#endif
diff --git a/shared/runtime/pyexec.h b/shared/runtime/pyexec.h
new file mode 100644
index 000000000..981e7dca9
--- /dev/null
+++ b/shared/runtime/pyexec.h
@@ -0,0 +1,59 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_UTILS_PYEXEC_H
+#define MICROPY_INCLUDED_LIB_UTILS_PYEXEC_H
+
+#include "py/obj.h"
+
+typedef enum {
+    PYEXEC_MODE_FRIENDLY_REPL,
+    PYEXEC_MODE_RAW_REPL,
+} pyexec_mode_kind_t;
+
+extern pyexec_mode_kind_t pyexec_mode_kind;
+
+// Set this to the value (eg PYEXEC_FORCED_EXIT) that will be propagated through
+// the pyexec functions if a SystemExit exception is raised by the running code.
+// It will reset to 0 at the start of each execution (eg each REPL entry).
+extern int pyexec_system_exit;
+
+#define PYEXEC_FORCED_EXIT (0x100)
+
+int pyexec_raw_repl(void);
+int pyexec_friendly_repl(void);
+int pyexec_file(const char *filename);
+int pyexec_file_if_exists(const char *filename);
+int pyexec_frozen_module(const char *name);
+void pyexec_event_repl_init(void);
+int pyexec_event_repl_process_char(int c);
+extern uint8_t pyexec_repl_active;
+
+#if MICROPY_REPL_INFO
+mp_obj_t pyb_set_repl_info(mp_obj_t o_value);
+MP_DECLARE_CONST_FUN_OBJ_1(pyb_set_repl_info_obj);
+#endif
+
+#endif // MICROPY_INCLUDED_LIB_UTILS_PYEXEC_H
diff --git a/shared/runtime/semihosting.c b/shared/runtime/semihosting.c
new file mode 100644
index 000000000..18c7f5d57
--- /dev/null
+++ b/shared/runtime/semihosting.c
@@ -0,0 +1,132 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Ayke van Laethem
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "semihosting.h"
+
+// Resources:
+// http://embed.rs/articles/2016/semi-hosting-rust/
+// https://wiki.dlang.org/Minimal_semihosted_ARM_Cortex-M_%22Hello_World%22
+// https://github.com/arduino/OpenOCD/blob/master/src/target/arm_semihosting.c
+
+#define SYS_OPEN   0x01
+#define SYS_WRITEC 0x03
+#define SYS_WRITE  0x05
+#define SYS_READC  0x07
+
+// Constants:
+#define OPEN_MODE_READ  (0) // mode "r"
+#define OPEN_MODE_WRITE (4) // mode "w"
+
+#ifndef __thumb__
+#error Semihosting is only implemented for ARM microcontrollers.
+#endif
+
+static int mp_semihosting_stdout;
+
+static uint32_t mp_semihosting_call(uint32_t num, const void *arg) {
+    // A semihosting call works as follows, similar to a SVCall:
+    //   * the call is invoked by a special breakpoint: 0xAB
+    //   * the command is placed in r0
+    //   * a pointer to the arguments is placed in r1
+    //   * the return value is placed in r0
+    // Note that because it uses the breakpoint instruction, applications
+    // will hang if they're not connected to a debugger. And they'll be
+    // stuck in a breakpoint if semihosting is not specifically enabled in
+    // the debugger.
+    // Also note that semihosting is extremely slow (sometimes >100ms per
+    // call).
+    register uint32_t num_reg __asm__ ("r0") = num;
+    register const void *args_reg __asm__ ("r1") = arg;
+    __asm__ __volatile__ (
+        "bkpt 0xAB\n"         // invoke semihosting call
+        : "+r" (num_reg)      // call number and result
+        : "r" (args_reg)      // arguments
+        : "memory");          // make sure args aren't optimized away
+    return num_reg; // r0, which became the result
+}
+
+static int mp_semihosting_open_console(uint32_t mode) {
+    struct {
+        char *name;
+        uint32_t mode;
+        uint32_t name_len;
+    } args = {
+        .name = ":tt",     // magic path to console
+        .mode = mode,      // e.g. "r", "w" (see OPEN_MODE_* constants)
+        .name_len = 3,     // strlen(":tt")
+    };
+    return mp_semihosting_call(SYS_OPEN, &args);
+}
+
+void mp_semihosting_init() {
+    mp_semihosting_stdout = mp_semihosting_open_console(OPEN_MODE_WRITE);
+}
+
+int mp_semihosting_rx_char() {
+    return mp_semihosting_call(SYS_READC, NULL);
+}
+
+static void mp_semihosting_tx_char(char c) {
+    mp_semihosting_call(SYS_WRITEC, &c);
+}
+
+uint32_t mp_semihosting_tx_strn(const char *str, size_t len) {
+    if (len == 0) {
+        return 0; // nothing to do
+    }
+    if (len == 1) {
+        mp_semihosting_tx_char(*str); // maybe faster?
+        return 0;
+    }
+
+    struct {
+        uint32_t fd;
+        const char *str;
+        uint32_t len;
+    } args = {
+        .fd = mp_semihosting_stdout,
+        .str = str,
+        .len = len,
+    };
+    return mp_semihosting_call(SYS_WRITE, &args);
+}
+
+uint32_t mp_semihosting_tx_strn_cooked(const char *str, size_t len) {
+    // Write chunks of data until (excluding) the first '\n' character,
+    // insert a '\r' character, and then continue with the next chunk
+    // (starting with '\n').
+    // Doing byte-by-byte writes would be easier to implement but is far
+    // too slow.
+    size_t start = 0;
+    for (size_t i = 0; i < len; i++) {
+        if (str[i] == '\n') {
+            mp_semihosting_tx_strn(str + start, i - start);
+            mp_semihosting_tx_char('\r');
+            start = i;
+        }
+    }
+    return mp_semihosting_tx_strn(str + start, len - start);
+}
diff --git a/shared/runtime/semihosting.h b/shared/runtime/semihosting.h
new file mode 100644
index 000000000..d053a03ed
--- /dev/null
+++ b/shared/runtime/semihosting.h
@@ -0,0 +1,51 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Ayke van Laethem
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_UTILS_SEMIHOSTING_H
+#define MICROPY_INCLUDED_LIB_UTILS_SEMIHOSTING_H
+
+/*
+
+To use semi-hosting for a replacement UART:
+- Add lib/semihosting/semihosting.c to the Makefile sources.
+- Call mp_semihosting_init() in main(), around the time UART is initialized.
+- Replace mp_hal_stdin_rx_chr and similar in mphalport.c with the semihosting equivalent.
+- Include lib/semihosting/semihosting.h in the relevant files.
+
+Then make sure the debugger is attached and enables semihosting.  In OpenOCD this is
+done with ARM semihosting enable followed by reset.  The terminal will need further
+configuration to work with MicroPython (bash: stty raw -echo).
+
+*/
+
+#include <stddef.h>
+#include <stdint.h>
+
+void mp_semihosting_init();
+int mp_semihosting_rx_char();
+uint32_t mp_semihosting_tx_strn(const char *str, size_t len);
+uint32_t mp_semihosting_tx_strn_cooked(const char *str, size_t len);
+
+#endif // MICROPY_INCLUDED_LIB_UTILS_SEMIHOSTING_H
diff --git a/shared/runtime/stdout_helpers.c b/shared/runtime/stdout_helpers.c
new file mode 100644
index 000000000..6a24cc2eb
--- /dev/null
+++ b/shared/runtime/stdout_helpers.c
@@ -0,0 +1,62 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2021 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <string.h>
+#include "py/mphal.h"
+
+/*
+ * Extra stdout functions
+ * These can be either optimized for a particular port, or reference
+ * implementation below can be used.
+ */
+
+// Send "cooked" string of given length, where every occurrence of
+// LF character is replaced with CR LF ("\n" is converted to "\r\n").
+// This is an optimised version to reduce the number of calls made
+// to mp_hal_stdout_tx_strn.
+void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {
+    const char *last = str;
+    while (len--) {
+        if (*str == '\n') {
+            if (str > last) {
+                mp_hal_stdout_tx_strn(last, str - last);
+            }
+            mp_hal_stdout_tx_strn("\r\n", 2);
+            ++str;
+            last = str;
+        } else {
+            ++str;
+        }
+    }
+    if (str > last) {
+        mp_hal_stdout_tx_strn(last, str - last);
+    }
+}
+
+// Send zero-terminated string
+void mp_hal_stdout_tx_str(const char *str) {
+    mp_hal_stdout_tx_strn(str, strlen(str));
+}
diff --git a/shared/runtime/sys_stdio_mphal.c b/shared/runtime/sys_stdio_mphal.c
new file mode 100644
index 000000000..e72facb98
--- /dev/null
+++ b/shared/runtime/sys_stdio_mphal.c
@@ -0,0 +1,175 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "py/obj.h"
+#include "py/stream.h"
+#include "py/mperrno.h"
+#include "py/mphal.h"
+
+// TODO make stdin, stdout and stderr writable objects so they can
+// be changed by Python code.  This requires some changes, as these
+// objects are in a read-only module (py/modsys.c).
+
+/******************************************************************************/
+// MicroPython bindings
+
+#define STDIO_FD_IN  (0)
+#define STDIO_FD_OUT (1)
+#define STDIO_FD_ERR (2)
+
+typedef struct _sys_stdio_obj_t {
+    mp_obj_base_t base;
+    int fd;
+} sys_stdio_obj_t;
+
+#if MICROPY_PY_SYS_STDIO_BUFFER
+STATIC const sys_stdio_obj_t stdio_buffer_obj;
+#endif
+
+void stdio_obj_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
+    sys_stdio_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_printf(print, "<io.FileIO %d>", self->fd);
+}
+
+STATIC mp_uint_t stdio_read(mp_obj_t self_in, void *buf, mp_uint_t size, int *errcode) {
+    sys_stdio_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    if (self->fd == STDIO_FD_IN) {
+        for (uint i = 0; i < size; i++) {
+            int c = mp_hal_stdin_rx_chr();
+            if (c == '\r') {
+                c = '\n';
+            }
+            ((byte *)buf)[i] = c;
+        }
+        return size;
+    } else {
+        *errcode = MP_EPERM;
+        return MP_STREAM_ERROR;
+    }
+}
+
+STATIC mp_uint_t stdio_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
+    sys_stdio_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    if (self->fd == STDIO_FD_OUT || self->fd == STDIO_FD_ERR) {
+        mp_hal_stdout_tx_strn_cooked(buf, size);
+        return size;
+    } else {
+        *errcode = MP_EPERM;
+        return MP_STREAM_ERROR;
+    }
+}
+
+STATIC mp_uint_t stdio_ioctl(mp_obj_t self_in, mp_uint_t request, uintptr_t arg, int *errcode) {
+    (void)self_in;
+    if (request == MP_STREAM_POLL) {
+        return mp_hal_stdio_poll(arg);
+    } else {
+        *errcode = MP_EINVAL;
+        return MP_STREAM_ERROR;
+    }
+}
+
+STATIC mp_obj_t stdio_obj___exit__(size_t n_args, const mp_obj_t *args) {
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(stdio_obj___exit___obj, 4, 4, stdio_obj___exit__);
+
+// TODO gc hook to close the file if not already closed
+
+STATIC const mp_rom_map_elem_t stdio_locals_dict_table[] = {
+    #if MICROPY_PY_SYS_STDIO_BUFFER
+    { MP_ROM_QSTR(MP_QSTR_buffer), MP_ROM_PTR(&stdio_buffer_obj) },
+    #endif
+    { MP_ROM_QSTR(MP_QSTR_read), MP_ROM_PTR(&mp_stream_read_obj) },
+    { MP_ROM_QSTR(MP_QSTR_readinto), MP_ROM_PTR(&mp_stream_readinto_obj) },
+    { MP_ROM_QSTR(MP_QSTR_readline), MP_ROM_PTR(&mp_stream_unbuffered_readline_obj)},
+    { MP_ROM_QSTR(MP_QSTR_readlines), MP_ROM_PTR(&mp_stream_unbuffered_readlines_obj)},
+    { MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mp_stream_write_obj) },
+    { MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&mp_identity_obj) },
+    { MP_ROM_QSTR(MP_QSTR___del__), MP_ROM_PTR(&mp_identity_obj) },
+    { MP_ROM_QSTR(MP_QSTR___enter__), MP_ROM_PTR(&mp_identity_obj) },
+    { MP_ROM_QSTR(MP_QSTR___exit__), MP_ROM_PTR(&stdio_obj___exit___obj) },
+};
+
+STATIC MP_DEFINE_CONST_DICT(stdio_locals_dict, stdio_locals_dict_table);
+
+STATIC const mp_stream_p_t stdio_obj_stream_p = {
+    .read = stdio_read,
+    .write = stdio_write,
+    .ioctl = stdio_ioctl,
+    .is_text = true,
+};
+
+STATIC const mp_obj_type_t stdio_obj_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_FileIO,
+    // TODO .make_new?
+    .print = stdio_obj_print,
+    .getiter = mp_identity_getiter,
+    .iternext = mp_stream_unbuffered_iter,
+    .protocol = &stdio_obj_stream_p,
+    .locals_dict = (mp_obj_dict_t *)&stdio_locals_dict,
+};
+
+const sys_stdio_obj_t mp_sys_stdin_obj = {{&stdio_obj_type}, .fd = STDIO_FD_IN};
+const sys_stdio_obj_t mp_sys_stdout_obj = {{&stdio_obj_type}, .fd = STDIO_FD_OUT};
+const sys_stdio_obj_t mp_sys_stderr_obj = {{&stdio_obj_type}, .fd = STDIO_FD_ERR};
+
+#if MICROPY_PY_SYS_STDIO_BUFFER
+STATIC mp_uint_t stdio_buffer_read(mp_obj_t self_in, void *buf, mp_uint_t size, int *errcode) {
+    for (uint i = 0; i < size; i++) {
+        ((byte *)buf)[i] = mp_hal_stdin_rx_chr();
+    }
+    return size;
+}
+
+STATIC mp_uint_t stdio_buffer_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
+    mp_hal_stdout_tx_strn(buf, size);
+    return size;
+}
+
+STATIC const mp_stream_p_t stdio_buffer_obj_stream_p = {
+    .read = stdio_buffer_read,
+    .write = stdio_buffer_write,
+    .ioctl = stdio_ioctl,
+    .is_text = false,
+};
+
+STATIC const mp_obj_type_t stdio_buffer_obj_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_FileIO,
+    .print = stdio_obj_print,
+    .getiter = mp_identity_getiter,
+    .iternext = mp_stream_unbuffered_iter,
+    .protocol = &stdio_buffer_obj_stream_p,
+    .locals_dict = (mp_obj_dict_t *)&stdio_locals_dict,
+};
+
+STATIC const sys_stdio_obj_t stdio_buffer_obj = {{&stdio_buffer_obj_type}, .fd = 0}; // fd unused
+#endif
diff --git a/shared/timeutils/timeutils.c b/shared/timeutils/timeutils.c
new file mode 100644
index 000000000..7c74f5fc3
--- /dev/null
+++ b/shared/timeutils/timeutils.c
@@ -0,0 +1,222 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2015 Daniel Campora
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/obj.h"
+
+#include "lib/timeutils/timeutils.h"
+
+// LEAPOCH corresponds to 2000-03-01, which is a mod-400 year, immediately
+// after Feb 29. We calculate seconds as a signed integer relative to that.
+//
+// Our timebase is relative to 2000-01-01.
+
+#define LEAPOCH ((31 + 29) * 86400)
+
+#define DAYS_PER_400Y (365 * 400 + 97)
+#define DAYS_PER_100Y (365 * 100 + 24)
+#define DAYS_PER_4Y   (365 * 4 + 1)
+
+STATIC const uint16_t days_since_jan1[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
+
+bool timeutils_is_leap_year(mp_uint_t year) {
+    return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
+}
+
+// month is one based
+mp_uint_t timeutils_days_in_month(mp_uint_t year, mp_uint_t month) {
+    mp_uint_t mdays = days_since_jan1[month] - days_since_jan1[month - 1];
+    if (month == 2 && timeutils_is_leap_year(year)) {
+        mdays++;
+    }
+    return mdays;
+}
+
+// compute the day of the year, between 1 and 366
+// month should be between 1 and 12, date should start at 1
+mp_uint_t timeutils_year_day(mp_uint_t year, mp_uint_t month, mp_uint_t date) {
+    mp_uint_t yday = days_since_jan1[month - 1] + date;
+    if (month >= 3 && timeutils_is_leap_year(year)) {
+        yday += 1;
+    }
+    return yday;
+}
+
+void timeutils_seconds_since_2000_to_struct_time(mp_uint_t t, timeutils_struct_time_t *tm) {
+    // The following algorithm was adapted from musl's __secs_to_tm and adapted
+    // for differences in MicroPython's timebase.
+
+    mp_int_t seconds = t - LEAPOCH;
+
+    mp_int_t days = seconds / 86400;
+    seconds %= 86400;
+    if (seconds < 0) {
+        seconds += 86400;
+        days -= 1;
+    }
+    tm->tm_hour = seconds / 3600;
+    tm->tm_min = seconds / 60 % 60;
+    tm->tm_sec = seconds % 60;
+
+    mp_int_t wday = (days + 2) % 7;   // Mar 1, 2000 was a Wednesday (2)
+    if (wday < 0) {
+        wday += 7;
+    }
+    tm->tm_wday = wday;
+
+    mp_int_t qc_cycles = days / DAYS_PER_400Y;
+    days %= DAYS_PER_400Y;
+    if (days < 0) {
+        days += DAYS_PER_400Y;
+        qc_cycles--;
+    }
+    mp_int_t c_cycles = days / DAYS_PER_100Y;
+    if (c_cycles == 4) {
+        c_cycles--;
+    }
+    days -= (c_cycles * DAYS_PER_100Y);
+
+    mp_int_t q_cycles = days / DAYS_PER_4Y;
+    if (q_cycles == 25) {
+        q_cycles--;
+    }
+    days -= q_cycles * DAYS_PER_4Y;
+
+    mp_int_t years = days / 365;
+    if (years == 4) {
+        years--;
+    }
+    days -= (years * 365);
+
+    /* We will compute tm_yday at the very end
+    mp_int_t leap = !years && (q_cycles || !c_cycles);
+
+    tm->tm_yday = days + 31 + 28 + leap;
+    if (tm->tm_yday >= 365 + leap) {
+        tm->tm_yday -= 365 + leap;
+    }
+
+    tm->tm_yday++;  // Make one based
+    */
+
+    tm->tm_year = 2000 + years + 4 * q_cycles + 100 * c_cycles + 400 * qc_cycles;
+
+    // Note: days_in_month[0] corresponds to March
+    STATIC const int8_t days_in_month[] = {31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31, 29};
+
+    mp_int_t month;
+    for (month = 0; days_in_month[month] <= days; month++) {
+        days -= days_in_month[month];
+    }
+
+    tm->tm_mon = month + 2;
+    if (tm->tm_mon >= 12) {
+        tm->tm_mon -= 12;
+        tm->tm_year++;
+    }
+    tm->tm_mday = days + 1; // Make one based
+    tm->tm_mon++;   // Make one based
+
+    tm->tm_yday = timeutils_year_day(tm->tm_year, tm->tm_mon, tm->tm_mday);
+}
+
+// returns the number of seconds, as an integer, since 2000-01-01
+mp_uint_t timeutils_seconds_since_2000(mp_uint_t year, mp_uint_t month,
+    mp_uint_t date, mp_uint_t hour, mp_uint_t minute, mp_uint_t second) {
+    return
+        second
+        + minute * 60
+        + hour * 3600
+        + (timeutils_year_day(year, month, date) - 1
+            + ((year - 2000 + 3) / 4) // add a day each 4 years starting with 2001
+            - ((year - 2000 + 99) / 100) // subtract a day each 100 years starting with 2001
+            + ((year - 2000 + 399) / 400) // add a day each 400 years starting with 2001
+            ) * 86400
+        + (year - 2000) * 31536000;
+}
+
+mp_uint_t timeutils_mktime_2000(mp_uint_t year, mp_int_t month, mp_int_t mday,
+    mp_int_t hours, mp_int_t minutes, mp_int_t seconds) {
+
+    // Normalize the tuple. This allows things like:
+    //
+    // tm_tomorrow = list(time.localtime())
+    // tm_tomorrow[2] += 1 # Adds 1 to mday
+    // tomorrow = time.mktime(tm_tomorrow)
+    //
+    // And not have to worry about all the weird overflows.
+    //
+    // You can subtract dates/times this way as well.
+
+    minutes += seconds / 60;
+    if ((seconds = seconds % 60) < 0) {
+        seconds += 60;
+        minutes--;
+    }
+
+    hours += minutes / 60;
+    if ((minutes = minutes % 60) < 0) {
+        minutes += 60;
+        hours--;
+    }
+
+    mday += hours / 24;
+    if ((hours = hours % 24) < 0) {
+        hours += 24;
+        mday--;
+    }
+
+    month--; // make month zero based
+    year += month / 12;
+    if ((month = month % 12) < 0) {
+        month += 12;
+        year--;
+    }
+    month++; // back to one based
+
+    while (mday < 1) {
+        if (--month == 0) {
+            month = 12;
+            year--;
+        }
+        mday += timeutils_days_in_month(year, month);
+    }
+    while ((mp_uint_t)mday > timeutils_days_in_month(year, month)) {
+        mday -= timeutils_days_in_month(year, month);
+        if (++month == 13) {
+            month = 1;
+            year++;
+        }
+    }
+    return timeutils_seconds_since_2000(year, month, mday, hours, minutes, seconds);
+}
+
+// Calculate the weekday from the date.
+// The result is zero based with 0 = Monday.
+// by Michael Keith and Tom Craver, 1990.
+int timeutils_calc_weekday(int y, int m, int d) {
+    return ((d += m < 3 ? y-- : y - 2, 23 * m / 9 + d + 4 + y / 4 - y / 100 + y / 400) + 6) % 7;
+}
diff --git a/shared/timeutils/timeutils.h b/shared/timeutils/timeutils.h
new file mode 100644
index 000000000..66e2a77f1
--- /dev/null
+++ b/shared/timeutils/timeutils.h
@@ -0,0 +1,105 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2015 Daniel Campora
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H
+#define MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H
+
+// The number of seconds between 1970/1/1 and 2000/1/1 is calculated using:
+// time.mktime((2000,1,1,0,0,0,0,0,0)) - time.mktime((1970,1,1,0,0,0,0,0,0))
+#define TIMEUTILS_SECONDS_1970_TO_2000 (946684800ULL)
+
+typedef struct _timeutils_struct_time_t {
+    uint16_t tm_year;       // i.e. 2014
+    uint8_t tm_mon;         // 1..12
+    uint8_t tm_mday;        // 1..31
+    uint8_t tm_hour;        // 0..23
+    uint8_t tm_min;         // 0..59
+    uint8_t tm_sec;         // 0..59
+    uint8_t tm_wday;        // 0..6  0 = Monday
+    uint16_t tm_yday;       // 1..366
+} timeutils_struct_time_t;
+
+bool timeutils_is_leap_year(mp_uint_t year);
+mp_uint_t timeutils_days_in_month(mp_uint_t year, mp_uint_t month);
+mp_uint_t timeutils_year_day(mp_uint_t year, mp_uint_t month, mp_uint_t date);
+
+void timeutils_seconds_since_2000_to_struct_time(mp_uint_t t,
+    timeutils_struct_time_t *tm);
+
+mp_uint_t timeutils_seconds_since_2000(mp_uint_t year, mp_uint_t month,
+    mp_uint_t date, mp_uint_t hour, mp_uint_t minute, mp_uint_t second);
+
+mp_uint_t timeutils_mktime_2000(mp_uint_t year, mp_int_t month, mp_int_t mday,
+    mp_int_t hours, mp_int_t minutes, mp_int_t seconds);
+
+// Select the Epoch used by the port.
+#if MICROPY_EPOCH_IS_1970
+
+static inline void timeutils_seconds_since_epoch_to_struct_time(uint64_t t, timeutils_struct_time_t *tm) {
+    // TODO this will give incorrect results for dates before 2000/1/1
+    return timeutils_seconds_since_2000_to_struct_time(t - TIMEUTILS_SECONDS_1970_TO_2000, tm);
+}
+
+static inline uint64_t timeutils_mktime(mp_uint_t year, mp_int_t month, mp_int_t mday, mp_int_t hours, mp_int_t minutes, mp_int_t seconds) {
+    return timeutils_mktime_2000(year, month, mday, hours, minutes, seconds) + TIMEUTILS_SECONDS_1970_TO_2000;
+}
+
+static inline uint64_t timeutils_seconds_since_epoch(mp_uint_t year, mp_uint_t month,
+    mp_uint_t date, mp_uint_t hour, mp_uint_t minute, mp_uint_t second) {
+    return timeutils_seconds_since_2000(year, month, date, hour, minute, second) + TIMEUTILS_SECONDS_1970_TO_2000;
+}
+
+static inline mp_uint_t timeutils_seconds_since_epoch_from_nanoseconds_since_1970(uint64_t ns) {
+    return ns / 1000000000ULL;
+}
+
+static inline uint64_t timeutils_nanoseconds_since_epoch_to_nanoseconds_since_1970(uint64_t ns) {
+    return ns;
+}
+
+#else // Epoch is 2000
+
+#define timeutils_seconds_since_epoch_to_struct_time timeutils_seconds_since_2000_to_struct_time
+#define timeutils_seconds_since_epoch timeutils_seconds_since_2000
+#define timeutils_mktime timeutils_mktime_2000
+
+static inline uint64_t timeutils_seconds_since_epoch_to_nanoseconds_since_1970(mp_uint_t s) {
+    return ((uint64_t)s + TIMEUTILS_SECONDS_1970_TO_2000) * 1000000000ULL;
+}
+
+static inline mp_uint_t timeutils_seconds_since_epoch_from_nanoseconds_since_1970(uint64_t ns) {
+    return ns / 1000000000ULL - TIMEUTILS_SECONDS_1970_TO_2000;
+}
+
+static inline int64_t timeutils_nanoseconds_since_epoch_to_nanoseconds_since_1970(int64_t ns) {
+    return ns + TIMEUTILS_SECONDS_1970_TO_2000 * 1000000000ULL;
+}
+
+#endif
+
+int timeutils_calc_weekday(int y, int m, int d);
+
+#endif // MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H
diff --git a/shared/upytesthelper/upytesthelper.c b/shared/upytesthelper/upytesthelper.c
new file mode 100644
index 000000000..326172be6
--- /dev/null
+++ b/shared/upytesthelper/upytesthelper.c
@@ -0,0 +1,126 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Linaro Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include <string.h>
+
+#include "py/mphal.h"
+#include "py/gc.h"
+#include "py/runtime.h"
+#include "py/compile.h"
+#include "upytesthelper.h"
+
+static const char *test_exp_output;
+static int test_exp_output_len, test_rem_output_len;
+static int test_failed;
+static void *heap_start, *heap_end;
+
+void upytest_set_heap(void *start, void *end) {
+    heap_start = start;
+    heap_end = end;
+}
+
+void upytest_set_expected_output(const char *output, unsigned len) {
+    test_exp_output = output;
+    test_exp_output_len = test_rem_output_len = len;
+    test_failed = false;
+}
+
+bool upytest_is_failed(void) {
+    if (test_failed) {
+        return true;
+    }
+    #if 0
+    if (test_rem_output_len != 0) {
+        printf("remaining len: %d\n", test_rem_output_len);
+    }
+    #endif
+    return test_rem_output_len != 0;
+}
+
+// MP_PLAT_PRINT_STRN() should be redirected to this function.
+// It will pass-thru any content to mp_hal_stdout_tx_strn_cooked()
+// (the dfault value of MP_PLAT_PRINT_STRN), but will also match
+// it to the expected output as set by upytest_set_expected_output().
+// If mismatch happens, upytest_is_failed() returns true.
+void upytest_output(const char *str, mp_uint_t len) {
+    if (!test_failed) {
+        if (len > test_rem_output_len) {
+            test_failed = true;
+        } else {
+            test_failed = memcmp(test_exp_output, str, len);
+            #if 0
+            if (test_failed) {
+                printf("failed after char %u, within %d chars, res: %d\n",
+                    test_exp_output_len - test_rem_output_len, (int)len, test_failed);
+                for (int i = 0; i < len; i++) {
+                    if (str[i] != test_exp_output[i]) {
+                        printf("%d %02x %02x\n", i, str[i], test_exp_output[i]);
+                    }
+                }
+            }
+            #endif
+            test_exp_output += len;
+            test_rem_output_len -= len;
+        }
+    }
+    mp_hal_stdout_tx_strn_cooked(str, len);
+}
+
+void upytest_execute_test(const char *src) {
+    // To provide clean room for each test, interpreter and heap are
+    // reinitialized before running each.
+    gc_init(heap_start, heap_end);
+    mp_init();
+    mp_obj_list_init(mp_sys_path, 0);
+    mp_obj_list_init(mp_sys_argv, 0);
+
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
+        qstr source_name = lex->source_name;
+        mp_parse_tree_t parse_tree = mp_parse(lex, MP_PARSE_FILE_INPUT);
+        mp_obj_t module_fun = mp_compile(&parse_tree, source_name, false);
+        mp_call_function_0(module_fun);
+        nlr_pop();
+    } else {
+        mp_obj_t exc = (mp_obj_t)nlr.ret_val;
+        if (mp_obj_is_subclass_fast(mp_obj_get_type(exc), &mp_type_SystemExit)) {
+            // Assume that sys.exit() is called to skip the test.
+            // TODO: That can be always true, we should set up convention to
+            // use specific exit code as skip indicator.
+            tinytest_set_test_skipped_();
+            goto end;
+        }
+        mp_obj_print_exception(&mp_plat_print, exc);
+        tt_abort_msg("Uncaught exception\n");
+    }
+
+    if (upytest_is_failed()) {
+        tinytest_set_test_failed_();
+    }
+
+end:
+    mp_deinit();
+}
diff --git a/shared/upytesthelper/upytesthelper.h b/shared/upytesthelper/upytesthelper.h
new file mode 100644
index 000000000..3a292befd
--- /dev/null
+++ b/shared/upytesthelper/upytesthelper.h
@@ -0,0 +1,37 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Linaro Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include "py/mpconfig.h"
+#include "lib/tinytest/tinytest.h"
+#include "lib/tinytest/tinytest_macros.h"
+
+void upytest_set_heap(void *start, void *end);
+void upytest_set_expected_output(const char *output, unsigned len);
+void upytest_execute_test(const char *src);
+void upytest_output(const char *str, mp_uint_t len);
+bool upytest_is_failed(void);