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Implement feature like wake lock in tickless design

Posted by redmilk525 on April 2, 2015

Hi, I'm using FreeRTOS 8.1.2 with tickless enabled via setting configUSETICKLESSIDLE to 1. There is a condition that my task is waiting an expected event in nearly future. If I put my task into suspend, then freertos may enter sleep and make my task missing this event. Here is possible solutions I've tried:

(1) Redefine macro configPRESLEEPPROCESSING and make it skip sleep if my task is waiting event. This is not a proper solution because this makes the tick count incorrect.

(2) Redefine macro configEXPECTEDIDLETIMEBEFORESLEEP as a function and return a huge number if my task is waiting event. But it's build fail in size check in FreeRTOS.h

Thus I think this condition need a feature like wake lock that if some process acquire wake lock then the system won't enter sleep. Is there a elegant way to achieve this feature without rewrite vPortSuppressTicksAndSleep or portTASK_FUNCTION()?


Implement feature like wake lock in tickless design

Posted by rtel on April 2, 2015

Here is possible solutions I've tried:

I don't think I understand the problem this is intended to be a solution to.

Which port are you using?

If you are using the Cortex-M port then an interrupt will unblock the task, so if the event you are waiting for comes from an interrupt (a reasonable assumption as the CPU is not running any code when it is in low power mode) then it will unblock in order to process the interrupt - and so not miss the event.

This is not a proper solution because this makes the tick count incorrect.

If you are using the Cortex-M port, or you have created your own following the examples, then the tick count will be corrected for whatever the time is when the suppress ticks and sleep function exits.

Thus I think this condition need a feature like wake lock that if some process acquire wake lock then the system won't enter sleep. Is there a elegant way to achieve this feature without rewrite vPortSuppressTicksAndSleep or portTASK_FUNCTION()?

That is what the existing configPRESLEEPPROCESSING macro allows you to do.

Regards.


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