Hi,
I've encountered problem with app timer functions being called from different interrupt levels. Looks like no memory error returned is caused by collision in underlaying atomic fifo library. This seems like unexpected behaviour as there is no information in documentation about such a behaviour.
Setup:
nRF5_SDK_17.1.0
gcc-arm-none-eabi-10-2020-q4-major (tested both windows and IOS)
gcc-arm-none-eabi-9-2019-q4-major (tested on IOS)
nRF52840_XXAA
App timer v2
no rtos
Originally encountered problem:
From main application thread SAADC was configured and started to perform conversion. After triggering SAADC operation app timer was started with purpose of generating timeout event for SAADC (we had previous problem with SAADC driver hangup and not handling interrupt properly). In SAADC driver event handler, app timer stop was called. App timer interrupt level was set to 7 and SAADC to 6. Randomly (due to SD and active BLE connection) when calling app timer start from main thread, NO_MEMORY error was returned. First investigation showed that app timer start and subsequent, underlaying rtc interrupt is again interrupted by SAADC callback. This interrupt of start operation scheduling caused it to return NO_MEMORY error.
I'm aware that NO_MEMORY error could be returned in case timer library has high load and operation queue is full. One of first solution was increasing timer operation queue from 10 to 20, however it didn't change anything, error was returned similarly frequent. Moreover, enabling app timer profiler (APP_TIMER_WITH_PROFILER=1) completely solved problem, as internally, queue element allocation (which was failing), is surrounded by critical section.
I've created simple project (zip will be attached to this ticket) that can reliably reproduce this issue.
To reproduce this problem slight modification was done in order not to use SAADC and simulate its delay (plus SD interrupt) with something more predictable. Instead of using SAADC, timer will be used, to get constant delay of interrupt. As timers are synchronous to 16MHz clock, we also have to synchronize test program with it. Main thread will be elevated to interrupt level 7, by additional timer. All other interrupts levels will be increased by 1 compared to original problem: app timer (rtc) to 6 and timer simulating SAADC to 5. Delay of simulating timer will be changed in loop and return code from app_timer_start will be monitored.
I was able to reproduce issue with different compilers and different optimization levels.
I haven't look deeper into it, but looks like reentrancy or other collision in atomic fifo is causing this issue. Or maybe I simply have something incorrectly configured.
Best regards
Tomasz
Tomasz
P.S. Regarding mentioned saadc driver problem, I will also create ticket when I will be able to reproduce it somehow reliably.
