FreeRTOS nrf_pwr_mgmt low power mode

[abhipray]

I am using FreeRTOS (sdk 15.2) configured to use RTC for the tick source and systick timer for the system. I am trying to put the device in a low power mode. I have tried two approaches:

1) One task running at priority higher than the idle task that makes calls to nrf_pwr_mgmt_feed() and nrf_pwr_mgmt_run().

2) Using the idle hook with tickless idle. The hook calls nrf_pwr_mgmt_feed()

In both setups, the device returns from WFE() immediately with NVIC->ISPR[0] set to IRQn 17 which is the RTC IRQn. I am also trying to analyze the CPU usage using nrf_pwr_mgmt which is 100% in both situations. Am I misconfiguring RTC or FreeRTOS somehow?

[Susheel Nuguru]

I am a bit confused, why are you using nrf_pwr_mgmt functions with tickless idle mode? shouldn't the tickless mode itself take care of the low power mode when the idle task is running?

[abhipray]

I am not calling nrf_pwr_mgmt_run() in the idle task hook. Just nrf_pwr_mgmt_feed() for the auto-shutdown feature, although it has no effect because the feature was turned off during testing. Ideally I would like to use the CPU usage monitoring as well but not sure how to accomplish that with the tickless idle.  

[Susheel Nuguru]

I do not think that you can use this feature with tickless idle (without editing port_cmsis_systick.c) file.

The CPU usage monitoring uses a debug pin which it sets before going to sleep and the tickless idle sleep does not do that. So you need to edit it to make it work.

[abhipray]

After diving into port_cmsis_systick and profiling the tasks, I realized that the tickless mode is actually working. I removed the nrf_pwr_mgmt entirely and implemented the CPU usage feature by defining functions for configPRE_SLEEP_PROCESSING and configPOST_SLEEP_PROCESSING that keep track of time spent in idle task.

[Susheel Nuguru]

Great. Thanks for letting us know