Writing to backup registers causes problems with the wake-up timer.
Here’s the situation. The system is built on the STM32WB5MM with basic code written using FreeRTOS. All works well, so now I add the BLE HeartRate application. If I prevent my code from running using a while (1) [ osDelay(10); } loop, the STM BLE Toolbox on my Android phone works fine displaying data. However, if I allow my code to run, the Toolbox connects, but no data is displayed. Pursuing this in my code, I determined that the wake-up interrupts were not occurring as they should.
By moving where I stop my code, I have narrowed it down to the following sequence:
HAL_PWR_EnableBkUpAccess();
HAL_RTCEx_BKUPWrite(&hrtc, RTC_BKP_DR19, Value);
HAL_PWR_DisableBkUpAccess();
If I simply comment out the last line allowing backup access to remain on. It also works. However, that leaves the backup registers vulnerable. (Note: I use this sequence frequently to protect data that must be retained through a power cycle. VBAT is provided by a coin cell. So, a general solution is preferable.)
This is the first I’ve worked with the wake-up timer. In researching this problem, I have not been able to determine that the “standard” code supporting the wake-up timers would pose any conflict like this.
Can anyone point me in any particular direction?