STM32H747 LPTIM4 PWM output in system STOP mode not working

[RChie.2]

Hi everyone, we have a problem using LPTIM4 PWM output on STM32H747I-DISCO when system enters STOP mode.

In this project, I need two independent PWM outputs with fixed frequency to work, while system goes to STOP mode to save power. LPTIM1_OUT & LPTIM4_OUT are used for this purpose.

■ The issue is:

1.In RUN mode, both LPTIM PWM works as expected.

2. After system enters STOP mode, LPTIM1_OUT keeps PWM output, as expected.

  But LPTIM4_OUT PWM stopped.

3. When system wakes up from STOP mode, LPTIM4 starts PWM generation again automatically. This behavior seems like normal timer, not low-power timer.

■ The waveform shown below helps to demonstrate the issue:

Red - LPTIM1_OUT

Yellow - LPTIM4_OUT

Green - MCU current consumption

■ Configuration codes are generated by STM32CubeIDE.

Some code excerpts:

A. Clock Source of LPTIM1 & LPTIM4 are LSE:

 PeriphClkInitStruct.Lptim1ClockSelection = RCC_LPTIM1CLKSOURCE_LSE;

 PeriphClkInitStruct.Lptim345ClockSelection = RCC_LPTIM345CLKSOURCE_LSE;

B. LPTIM init Functions

// ------------------------ LPTIM Init Functions ----------------------------
static void MX_LPTIM1_Init(void)
{
 hlptim1.Instance = LPTIM1;
 hlptim1.Init.Clock.Source = LPTIM_CLOCKSOURCE_APBCLOCK_LPOSC;
 hlptim1.Init.Clock.Prescaler = LPTIM_PRESCALER_DIV1;
 hlptim1.Init.Trigger.Source = LPTIM_TRIGSOURCE_SOFTWARE;
 hlptim1.Init.OutputPolarity = LPTIM_OUTPUTPOLARITY_LOW;
 hlptim1.Init.UpdateMode = LPTIM_UPDATE_IMMEDIATE;
 hlptim1.Init.CounterSource = LPTIM_COUNTERSOURCE_INTERNAL;
 hlptim1.Init.Input1Source = LPTIM_INPUT1SOURCE_GPIO;
 hlptim1.Init.Input2Source = LPTIM_INPUT2SOURCE_GPIO;
 if (HAL_LPTIM_Init(&hlptim1) != HAL_OK)
 {
 Error_Handler();
 }
}
 
static void MX_LPTIM4_Init(void)
{
 hlptim4.Instance = LPTIM4;
 hlptim4.Init.Clock.Source = LPTIM_CLOCKSOURCE_APBCLOCK_LPOSC;
 hlptim4.Init.Clock.Prescaler = LPTIM_PRESCALER_DIV1;
 hlptim4.Init.Trigger.Source = LPTIM_TRIGSOURCE_SOFTWARE;
 hlptim4.Init.OutputPolarity = LPTIM_OUTPUTPOLARITY_LOW;
 hlptim4.Init.UpdateMode = LPTIM_UPDATE_IMMEDIATE;
 hlptim4.Init.CounterSource = LPTIM_COUNTERSOURCE_INTERNAL;
 if (HAL_LPTIM_Init(&hlptim4) != HAL_OK)
 {
 Error_Handler();
 }
}

C. Start PWM generation:

 HAL_LPTIM_PWM_Start(&hlptim1, 32767, 16383);

 HAL_LPTIM_PWM_Start(&hlptim4, 32767, 16383);

D. To enter system STOP mode:

 HAL_PWREx_ConfigD3Domain(PWR_D3_DOMAIN_STOP);

 HAL_PWREx_EnterSTOPMode( PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFI, PWR_D3_DOMAIN);

 HAL_PWREx_EnterSTOPMode( PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI, PWR_D1_DOMAIN);

[RChie.2]

Sorry, this issue has been fixed after adding these two lines in LPTIM4_Init:

 __HAL_RCC_LPTIM4_CLKAM_ENABLE();

 __HAL_RCC_LPTIM4_CLK_SLEEP_ENABLE();

This requirement is described in RM0399, P.408:

"In order for the LPTIMER to operate with lse_ck or lsi_ck when the circuit is in STOP mode, the user application has to select the lsi_ck or lse_ck input via LPTIMxSEL fields, and set bit LPTIMxAMEN and LPTIMxLPEN to '1'."

** LPTIMxLPEN is enabled by default, while 'LPTIM1AMEN' does not exist since it is not located in D3 domain.

[Imen.D]

Hello @RChie.2​ and thanks for sharing the solution.

I marked your answer as "Best Answer", this can be very helpful for Community users to find this solution more quickly.

Imen