rp2: Make rp2_state_machine_exec accept integers.

Currently rp2.StateMachine.exec(instr_in) requires that the instr_in
parameter be a string representing the PIO assembly language instruction
to be encoded by rp2.asm_pio_encode(). This commit allows the parameter
to also be of integral type. This is useful if the exec() method is
being called often where the use of pre-encoded machine code is
desireable.

This commit still supports calls like:
    sm.exec("set(0, 1)")

It also now supports calls like:
    # Performed once earlier, maybe in __init__()
    assembled_instr = rp2.asm_pio_encode("out(y, 8)", 0)
    # Performed multiple times later as the PIO state machine is
    # configured for its next run.
    sm.exec(assembled_instr)

The existing examples/rp2/pio_exec.py and examples/rp2/pio_pwm.py that
exercise the rp2.StateMachine.exec() method still work with this change.

Signed-off-by: Adam Green <adamgrym@yahoo.com>

2 files changed, 22 insertions, 12 deletions

diff --git a/docs/library/rp2.StateMachine.rst b/docs/library/rp2.StateMachine.rst
index d39194e6f..ee16ce3c5 100644
--- a/docs/library/rp2.StateMachine.rst
+++ b/docs/library/rp2.StateMachine.rst
@@ -82,11 +82,18 @@ Methods
 
 .. method:: StateMachine.exec(instr)
 
-    Execute a single PIO instruction. Uses `asm_pio_encode` to encode the
-    instruction from the given string *instr*.
+    Execute a single PIO instruction.
+
+    If *instr* is a string then uses `asm_pio_encode` to encode the instruction
+    from the given string.
 
     >>> sm.exec("set(0, 1)")
 
+    If *instr* is an integer then it is treated as an already encoded PIO
+    machine code instruction to be executed.
+
+    >>> sm.exec(rp2.asm_pio_encode("out(y, 8)", 0))
+
 .. method:: StateMachine.get(buf=None, shift=0)
 
     Pull a word from the state machine's RX FIFO.
diff --git a/ports/rp2/rp2_pio.c b/ports/rp2/rp2_pio.c
index 3ece26bd4..2e3047525 100644
--- a/ports/rp2/rp2_pio.c
+++ b/ports/rp2/rp2_pio.c
@@ -684,16 +684,19 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(rp2_state_machine_restart_obj, rp2_state_machin
 // StateMachine.exec(instr)
 STATIC mp_obj_t rp2_state_machine_exec(mp_obj_t self_in, mp_obj_t instr_in) {
     rp2_state_machine_obj_t *self = MP_OBJ_TO_PTR(self_in);
-    mp_obj_t rp2_module = mp_import_name(MP_QSTR_rp2, mp_const_none, MP_OBJ_NEW_SMALL_INT(0));
-    mp_obj_t asm_pio_encode = mp_load_attr(rp2_module, MP_QSTR_asm_pio_encode);
-    uint32_t sideset_count = self->pio->sm[self->sm].pinctrl >> PIO_SM0_PINCTRL_SIDESET_COUNT_LSB;
-    uint8_t sideset_opt = !!(self->pio->sm[self->sm].execctrl & (1 << PIO_SM0_EXECCTRL_SIDE_EN_LSB));
-    mp_obj_t args[3];
-    args[0] = instr_in;
-    args[1] = MP_OBJ_NEW_SMALL_INT(sideset_count);
-    args[2] = MP_OBJ_NEW_SMALL_INT(sideset_opt);
-    mp_obj_t encoded_obj = mp_call_function_n_kw(asm_pio_encode, 3, 0, args);
-    mp_int_t encoded = mp_obj_get_int(encoded_obj);
+    mp_int_t encoded = 0;
+    if (!mp_obj_get_int_maybe(instr_in, &encoded)) {
+        mp_obj_t rp2_module = mp_import_name(MP_QSTR_rp2, mp_const_none, MP_OBJ_NEW_SMALL_INT(0));
+        mp_obj_t asm_pio_encode = mp_load_attr(rp2_module, MP_QSTR_asm_pio_encode);
+        uint32_t sideset_count = self->pio->sm[self->sm].pinctrl >> PIO_SM0_PINCTRL_SIDESET_COUNT_LSB;
+        uint8_t sideset_opt = !!(self->pio->sm[self->sm].execctrl & (1 << PIO_SM0_EXECCTRL_SIDE_EN_LSB));
+        mp_obj_t args[3];
+        args[0] = instr_in;
+        args[1] = MP_OBJ_NEW_SMALL_INT(sideset_count);
+        args[2] = MP_OBJ_NEW_SMALL_INT(sideset_opt);
+        mp_obj_t encoded_obj = mp_call_function_n_kw(asm_pio_encode, 3, 0, args);
+        encoded = mp_obj_get_int(encoded_obj);
+    }
     pio_sm_exec(self->pio, self->sm, encoded);
     return mp_const_none;
 }