Some event prevent the uC to enter low power mode

RE: Some event prevent the uC to enter low power mode

Jose Xavier — Wed, 09 Jan 2019 08:38:37 GMT

"However, if it is required (for testing or for other purposes) to demonstrate a guaranteed period of sleep caused by WFE - and assuming that the processor does implement WFE sleep behavior - the following approach can be used.

If you are not executing any instructions which can cause exceptions (eg. LDR/STR, SVC) and you do not have any asynchronous sources of exceptions active (NMI, INTISR, SysTick) and you do not have a debugger attached which could issue a debug HALT, then there is nothing to cause the event register to become set unexpectedly.

In this scenario, you can use the sequence:

SEV WFE WFE

The SEV will set the event register, causing the first WFE to complete execution immediately. The second WFE will then be executed with the event register cleared, and in the absence of any of the other possible mechanisms for setting the event register, this will put the processor to sleep until the RXEV input goes HIGH."

In the bottom of the page it says that is possible to make it sleep with the above sequence.

RE: Some event prevent the uC to enter low power mode

Jose Xavier — Wed, 09 Jan 2019 08:29:34 GMT

I want it to sleep on some specific states.

RE: Some event prevent the uC to enter low power mode

Stian Røed Hafskjold — Wed, 09 Jan 2019 07:50:02 GMT

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15506.html

"Typically, sleep will take place when the processor loops around and re-executes the WFE instruction. The processor may wake up for spurious reasons from this spinlock sleep before the spinlock condition is eventually satisfied, but placing the WFE in the loop allows the processor to return to the sleeping condition repeatedly until the condition is met."

RE: Some event prevent the uC to enter low power mode

Stian Røed Hafskjold — Wed, 09 Jan 2019 07:46:25 GMT

Sorry I don't know what you are trying to accomplish, but normal programming practice is to put WFE in your main loop. Then the CPU will wake up to whatever event causing an interrupt, act upon it if there's a handler for the interrupt, and then go back to idle state. And repeat infinitely.

RE: Some event prevent the uC to enter low power mode

Jose Xavier — Mon, 07 Jan 2019 17:48:50 GMT

why?

If I put 4 WFE on the code above it works.

RE: Some event prevent the uC to enter low power mode

Stian Røed Hafskjold — Mon, 07 Jan 2019 12:15:59 GMT

You must put the WFE call in the main loop