STM32WB55 LPTIM PWM from LSE appears broken.

[JWieb]

I am trying to get my STM32WB5MM-DK to output a PWM from LPTIM1 clocked from LSE in STOP mode.

I created a fresh project with STM32SCUBEIDE selecting HSI clock for the main CPU and LSE clock for the LPTIM1.

Then in User Code 2 section i put the following:

  LL_C2_PWR_SetPowerMode(LL_PWR_MODE_SHUTDOWN); //Shutdown CPU2
 
  HAL_LPTIM_PWM_Start(&hlptim1, 999, 499);//DIV2 = ~16.4HZ 50% Duty
 
  HAL_Delay(500); //PWM can be seen on scope here
 
  HAL_PWREx_EnterSTOP0Mode(PWR_STOPENTRY_WFI); //PWM stops

However when i get to the stop mode, the pwm signal stops... what am i doing wrong?

[Peter BENSCH · Accepted solution]

Of course, you have to be careful where you are clocking the LPTIM1 from. In the RM0434 you will find the note:

If the LPTIM is clocked by an oscillator available in Stop mode, LPTIM is functional and the interrupts cause the device to exit the Stop mode.

Regards

/Peter

[JWieb]

Hi Peter,

Thank you for the prompt reply. After playing with this for a bit my problem was the pesky SysTick. Simply adding:

HAL_SuspendTick();

Fixed my issue.

However I do find it weird that the PWM of LPTIM1 would stop from this. Perhaps a hard fault was being generated?