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Zephyr's k_sleep gets stuck on nRF52832


Kimberly Langland <KimL@...>
 

Hello All,

 

We were seeing an issue that occasionally, all tasks waiting for a timeout using k_sleep get stuck in the suspended state (while other tasks continue to run normally), and then after about 8 minutes full normal functionality returns.

 

After digging into this issue, is appears that either the RTC needs an N+3 buffer between the RTC->COUNTER and the RTC->CC value to guarantee to trigger the ISR (instead of an N+2 buffer as documented), or that there is a race condition in the nrf_rtc_timer driver where between the time of reading the RTC->COUNTER, and writing to RTC->CC, RTC->COUNTER has already advanced.

 

Has anyone else seen this, or know the appropriate fix/workaround?

 

 

 

Detailed description:

* Zephyr Version: 1.14.99

* Running on nR53832

 

Each time this behavior occurs, the first task in the timeout_list (in the kernel/timeout module) has a timeout time of 1 tick. Reading the RTC1 registers, directly as this occurs, the RTC1->COUNTER value is just above the RCT1->CC[0] value. Normal behavior returns about 8 mins later when the RTC1->COUNTER register passes the RTC1->CC[0] value a second time (this is a 24 bit register clocked at 32kHZ with no prescaler).

 

In Nordic's documentation for the RTC on nRF52832 it states: "If the COUNTER is N, writing N+2 to a CC register is guaranteed to trigger a COMPARE event at N+2". Zephyrs driver seems to address this case by writing N+2 to the RTC1->CC[0] register (instead on N+1) in the case that a one tick timeout is requested. However in this case we are still not receiving the ISR until the COUNTER has looped around.

 

I have tried setting the RTC1->CC[0] register instead to N+3 (in the 1 tick timeout case), and have not yet seen the issue reoccur with the following modification to the nrf_rtc_timer driver.

 

/* dt - is the delta between RTC->COUNTER and RTC->CC[0]

* cyc - is the value to write to RTC->CC[0] */

} else if (dt == 1) {

-    set_comparator(cyc + 1);

+    set_comparator(cyc + 2);

}

 

 

 

Kimberly Langland
Sr. Firmware Engineer
Product Innovation Center
Nytec.com

425.947.2676

 

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Peter A. Bigot
 

Version 1.14.99 suggests you have a snapshot of the development series leading up to the recent 2.0 release.  The problem you're reporting was fixed in #17845 in upstream Zephyr 2019-08-01.  It may be worth updating to the 2.0 release for your development as many other problems were fixed in the latter part of August.

Peter