STM32F401RE Board PWM doesn't work on this port

[CMcC.1]

Hi everyone

I have an STM32F401RE board and I have an LED from pin PB6 to GND.

In the same project that this snippet code below comes from I have a PWM running on PA5 pin and it is blinking.

I have been at this all night and I can't figure out why PB6 is not blinking with the PWM. Here is the code. I am using Timer5 and as far as I know the AFR[0] is set correctly.

I hope anybody can see something wrong cause if not then I really don't know what to do : /

Also another question is.. if I want to start and stop the PWM output on that pin instantly and on a regular basis what would be the best way to do so? Disable the PWM or reset the PORT MODE to something else?

Thanks

void step_init(){
	RCC->AHB1ENR |= (1 << 2); //Enable clock access to port B
 
	GPIOB->AFR[0] |= (1<<25); //Set PB6 for TIM5
	GPIOB->MODER |= (1<<13); //Sets oub PB6 for alternate functions
	//Timer Setup
 
	RCC->APB1ENR |= (1<<3); //Enables Timer5
	TIM5->PSC = 1600-1; //Prescaker of 1600
	TIM5->ARR = 10000; //Reload at 10000 counts
	TIM5->CNT = 0; //
	TIM5->CCMR1 = 0b1100100; //OC1M PWM Mode1 and Output compare 1 preload enable
	//TIM5->CCMR1 = 0x0060; // Enable PWM mode //1100000
	TIM5->CCER |= 1; //Enable PWM ch1
	TIM5->CCR1 = 5000; //50%DC
	TIM5->CR1 |= 1; //Enable
}

[TDK]

You need to wait a few cycles between enabling the clock and actually using the peripheral. It's possible that is causing the issue.

Best way to start/stop PWM would be to start/stop the timer, IMO. Set/clear the CR1_EN bit, and reset CNT to 0 if needed.

[CMcC.1]

Ok I followed your advice and it works great now thanks allot!

[waclawek.jan]

> RCC->AHB1ENR |= (1 << 2); //Enable clock access to port B

That enables GPIOC and not GPIOB.

Also, there's no TIM5 channel on PB6; there is TIM4_CH1 at AF2 - see Alternate function mapping table in Datasheet.

You might want to use the symbols defined in the CMSIS-mandated device header (you are using them anyway, RCC, TIM5 etc. come from that header too).

As TDK said, you may want to make a delay between enabling clock to a peripheral and using that peripheral, see Delay after an RCC peripheral clock enabling erratum; tht time best to be utilized for enabling other clocks:

RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN; // enable GPIOB clock
RCC->APB1ENR |= RCC_APB1ENR_TIM4EN; // enable TIM4 clock
GPIOB->AFR[0] |= 2 << GPIO_AFRL_AFSEL6_Pos; // set PB6 for AF2 = TIM4_CH1
GPIOB->MODER |= 0b10 << GPIO_MODER_MODE6_Pos; // set PB6 to AF
etc.

The preload bit in TIMx_CCMRx is bit 3, not bit 2:

TIM4->CCMR1 = 0
 | (0b00 << TIM_CCMR1_CC1S_Pos) // set CH1 to Compare
 | (0b110 << TIM_CCMR1_OC1M_Pos) // set CH1 to PWM1
 | TIM_CCMR1_OC1PE // enable preload for CH1
;

Note, that the value you've set into CCR1 gets active only after the first period (which is also shorter due to PSC being implicitly preloaded, too)

JW

[CMcC.1]

Thanks allot for the input.

I just want to try bare metal before I jump into the MCU Specific headers etc.

I will eventually get there of course.

I somehow missed that its set to TIM5 and not 4.

Thanks it is working now.

[CMcC.1]

Thanks allot for the input.

I just want to try bare metal before I jump into the MCU Specific headers etc.

I will eventually get there of course.

I somehow missed that its set to TIM5 and not 4.

Thanks it is working now.