PWM no signal

[Marrkinho]

I've wrote a code without using Hal to produce a signal on the scope but i'm not getting any signal on my pin.

This is on a NUCLEO F401RE. Using TIMER3_CHANNEL1 and GPIOB for my Alternate function.

#include <stdint.h>

#include "stm32f4xx.h"

#include "stm32f401xe.h"

#define CMS_6 (1U<<6)

#define CMS_5 (1U<<5)

int main(void)

{

//Enable clock access to TIMER3/PWM

RCC->AHB1ENR |= (1U<<1); //GPIO Port B enable

RCC->APB1ENR |= (1U<<1); //Timer clock enable

//Set alternate function mode PB4(D5)

GPIOB->MODER |= (1U<<9);

GPIOB->MODER&=~ (1U<<8);

GPIOB->AFR[0]|= (1U<<18);

//Enable Timer

TIM3->CR1 |= (1U<<0)|(1U<<7); // Counter Enable , 

TIM3->CR1 &=~CMS_6 ;/*Edge aligned mode

TIM3->CR1 &=~CMS_5;                     */

TIM3->CR1 &=~ (1U<<4);// Direction Enable used as upconter 

//Setting PWM mode 1 (OC1M),(OC1PE)

TIM3->CCMR1 |=((1U<<6)|(1U<<5))| (1U<<3);

//Event Generation register

TIM3->EGR |= (1<<0);

//Capture Compare enable register/Enabled Channel 1

TIM3->CCER |= (1U<<1);

//PWM frequency  = Frequency clock/PSC/ARR 42Mhz/1000

//PWM Duty cycle = CCR1/ARR = 50% Duty cycle.

TIM3->PSC  =42;

TIM3->ARR  = 1000;

TIM3->CCR1 = 500;  //Duty cycle 50% , counting from 0 to a 1000;

for(;;);

}

[AScha.3]

>I've wrote a code without using Hal to produce a signal on the scope but i'm not getting any signal 

So use Cube/HAL , to see, how its done. Even if you dont like it.

[waclawek.jan]

Read out and check/post content of TIM and relevant GPIO registers.

> GPIOB->AFR[0]|= (1U<<18);

This sets AFR for PB4 to 0b0100 = 4, that's not what you want.

JW

[Marrkinho]

This is a reference of the datasheet. The reset values are 0's hence, I am trying to SET pin 18 and leave the rest to 0 as highlighted. Not sure what  you meant by saying that's not what I want ? Any further explanation would be helpful . Thanks

[Tesla DeLorean · Accepted solution]

Is the goal to write the most inefficient code, that's hard to maintain too?

TIM3_CH1 is AF2 on PB4

ARR and PSC are set as N-1 values

[Marrkinho]

I've made changes and took on your advice , wasn't getting a signal still when I run it . I know when using CUBE/HAL you need to set the clock config tree, and as I'm writing manually I don't have anything set for it ,could that be the issue?

[waclawek.jan]

You should have some output without configuring the clocks in RCC, too, as the whole mcu runs out of the default HSI RC oscillator at 16MHz.

Read out and check/post content of TIM and relevant GPIO registers.

JW

[gbm]

How about:

TIM3->CCER = TIM_CCER_CC1E;

Use bit names instead of magic numbers!

Also, timer clock frequency is 84 MHz (2 x ABP1 frequency).

[waclawek.jan]

Nice catch!

JW