Low Power Support For ARM Cortex-M

jiangtianyu007 wrote on Tuesday, July 21, 2015:

In freertosv8.2.1\freertos\source\portable\iar\arm_cm3, I have a question about the __weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime ) function.

line 408: /* Enter a critical section but don’t use the taskENTER_CRITICAL()
method as that will mask interrupts that should exit sleep mode. */

vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime ) means disable other interrupt except for systick, and use systick to wake up mcu from sleep mode.

but in my opinion, __disable_interrupt() is IAR intrinsic function, and equal with cpsid i. It means any interrupt which priority below 0(logically) will be disabled. So how can systick wake MCU up?

rtel wrote on Tuesday, July 21, 2015:

This information is provided in the Cortex-M technical reference manual, from ARM, so is not really a software question - however the answer is that interrupts will still bring the CPU out of sleep mode even when they are globally disabled in the core.

jiangtianyu007 wrote on Tuesday, July 21, 2015:

Is your mean that even the systick interrupt is masked, systick also will wake MCU up ? If so, the system will not enter the systick handler, just only bring CPU out of sleep mode. Is it right?

rtel wrote on Tuesday, July 21, 2015:


Please read the hardware documentation.

jiangtianyu007 wrote on Wednesday, July 22, 2015:

Thanks very much.