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Low Power Support For ARM Cortex-M

Posted by jiangtianyu007 on July 21, 2015

In freertosv8.2.1freertossourceportableiararmcm3, I have a question about the __weak void vPortSuppressTicksAndSleep( TickTypet xExpectedIdleTime ) function.

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

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, _disableinterrupt() 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?


Low Power Support For ARM Cortex-M

Posted by rtel on 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.


Low Power Support For ARM Cortex-M

Posted by jiangtianyu007 on 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?


Low Power Support For ARM Cortex-M

Posted by rtel on July 21, 2015

Yes.

Please read the hardware documentation.


Low Power Support For ARM Cortex-M

Posted by jiangtianyu007 on July 22, 2015

Thanks very much.


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