Clock scaling ------------- The kernel supports scaling of CLCK.CMODE, CLCK.CM and CLKC.P0 clock registers. If built with CONFIG_PM and CONFIG_SYSCTL options enabled, four extra files will appear in the directory /proc/sys/pm/. Reading these files will show: p0 -- current value of the P0 bit in CLKC register. cm -- current value of the CM bits in CLKC register. cmode -- current value of the CMODE bits in CLKC register. On all boards, the 'p0' file should also be writable, and either '1' or '0' can be rewritten, to set or clear the CLKC_P0 bit respectively, hence controlling whether the resource bus rate clock is halved. The 'cm' file should also be available on all boards. '0' can be written to it to shift the board into High-Speed mode (normal), and '1' can be written to shift the board into Medium-Speed mode. Selecting Low-Speed mode is not supported by this interface, even though some CPUs do support it. On the boards with FR405 CPU (i.e. CB60 and CB70), the 'cmode' file is also writable, allowing the CPU core speed (and other clock speeds) to be controlled from userspace. Determining current and possible settings ----------------------------------------- The current state and the available masks can be found in /proc/cpuinfo. For example, on the CB70: # cat /proc/cpuinfo CPU-Series: fr400 CPU-Core: fr405, gr0-31, BE, CCCR CPU: mb93405 MMU: Prot FP-Media: fr0-31, Media System: mb93091-cb70, mb93090-mb00 PM-Controls: cmode=0xd31f, cm=0x3, p0=0x3, suspend=0x9 PM-Status: cmode=3, cm=0, p0=0 Clock-In: 50.00 MHz Clock-Core: 300.00 MHz Clock-SDRAM: 100.00 MHz Clock-CBus: 100.00 MHz Clock-Res: 50.00 MHz Clock-Ext: 50.00 MHz Clock-DSU: 25.00 MHz BogoMips: 300.00 And on the PDK, the PM lines look like the following: PM-Controls: cm=0x3, p0=0x3, suspend=0x9 PM-Status: cmode=9, cm=0, p0=0 The PM-Controls line, if present, will indicate which /proc/sys/pm files can be set to what values. The specification values are bitmasks; so, for example, "suspend=0x9" indicates that 0 and 3 can be written validly to /proc/sys/pm/suspend. The PM-Controls line will only be present if CONFIG_PM is configured to Y. The PM-Status line indicates which clock controls are set to which value. If the file can be read, then the suspend value must be 0, and so that's not included.