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I have an STM32L476 Discovery Board. I'm trying to generate a PWM signal on the GPIO pin PE14 using TIM1_CH4 using bare-metal in CubeIDE.

I have created a new project in Cube and have kept the default System Clock Configuration. My aim is to have a duty cycle of 50%. I have prescaled by 79 in order to set the Timer Clock frequency at 1MHz.

I have gone through the Datasheet, Reference Manual, and Timer Cookbook several times but for some reason, I can't get it to work. Is there something that I have overlooked in my code?

void intialize_gpioe(void){
    RCC->AHB2ENR |= RCC_AHB2ENR_GPIOEEN;    // GPIOE clock enable
    GPIOE->MODER &= ~GPIO_MODER_MODER14;  // Configure PE14 as Alternative Function.
    GPIOE->MODER |= ~GPIO_MODER_MODER14_1;
    GPIOE->AFR[1] &= ~GPIO_AFRH_AFRH6; // PE14 configured as AF1: TIM1_CH4
    GPIOE->AFR[1] |= 0x01000000;
}

void initalize_tim1(void){
    intialize_gpioe();
    RCC->APB2ENR |= RCC_APB2ENR_TIM1EN; // TIM1 timer clock enable
    TIM1->PSC = 79; // Set Prescaler to 1MHz
    TIM1->ARR = 100;
    TIM1-> CCR4 = 50;
    TIM1->CCMR2 &= ~TIM_CCMR2_CC4S; // CC4 channel is configured as output
    TIM1->CCER &= ~TIM_CCER_CC4P;   // Output Polarity set to Active High
    TIM1->CCMR2 &= ~TIM_CCMR2_OC4M; // Output Compare 4 Mode set as PWM Mode 1.
    TIM1->CCMR2 |= TIM_CCMR2_OC4M_1 | TIM_CCMR2_OC4M_2; // Output Compare 4 Mode set as PWM Mode 1.
    TIM1->CCMR2 |= TIM_CCMR2_OC4PE; // Enable the corresponding preload register
    TIM1->CCER |= TIM_CCER_CC4E; // Capture/Compare 4 Output Enable
    TIM1->EGR |= TIM_EGR_UG;    // Before starting the counter, you have to initialize all the registers
    TIM1->BDTR |= TIM_BDTR_MOE;
    TIM1->CR1 |= TIM_CR1_CEN; // Start Timer
}
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  • \$\begingroup\$ Can you describe "can't get it to work"? Does it fail to work? What's the error message? Does it crash at run-time? Does it behave differently than expected? If so, what do you expect to happen and what happens instead? \$\endgroup\$ – Codo Sep 24 '20 at 6:10
  • \$\begingroup\$ what exactly do you mean by bare-metal? \$\endgroup\$ – jsotola Sep 24 '20 at 7:16
  • \$\begingroup\$ you have to enable ARR preload in the CR1 register. it's a must for pwm generation according to the reference manual I read earlier. (I'm answering based on another model) \$\endgroup\$ – Tirdad Sadri Nejad Sep 24 '20 at 11:53
  • \$\begingroup\$ @Codo No errors in the code. But no signal appears on the pin. I know the pin works because I have a separate project to specifically test the pwm on this pin using HAL. \$\endgroup\$ – Jonathan Pereira Sep 24 '20 at 12:43
  • \$\begingroup\$ @jsotola In my case, bare-metal would be register configuration with bitmasking without HAL functions. \$\endgroup\$ – Jonathan Pereira Sep 24 '20 at 12:45
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The GPIO Alternative function configuration is incorrect:

GPIOE->MODER |= ~GPIO_MODER_MODER14_1;

The correct configuration is:

GPIOE->MODER |= GPIO_MODER_MODER14_1;
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