STM32F4-PWM输出以控制伺服

Question

So I'm trying to move a servo with an STM32F4 discovery board. My code is below.

As far as I can see, everything is set up correctly, but I'm not getting any output on pin PC6. Can anyone spot what I've done wrong/point me in the right direction?

Thanks!

#include <stm32f4xx.h>
//#include "stm32f4xx_tim.h"

#define  RCC_APB1ENR_TIM3EN          ((uint32_t)0x00000002)


void delay (void)                   //create simple delay loop
{
int d;
for (d=0; d<10000000; d++);
}

int main (void)
{

    RCC->APB1ENR     = RCC_APB1ENR_TIM3EN;  //enable timer 3
TIM3->CR1       |= 0x81;                    //enable timer 1 = 10000001
//TIM3->CR2         |= 0x40;                                    //                              = 01000000
TIM3->PSC        = 0x48;                                //set prescale to 72
TIM3->ARR        = 0x4E20;                          //set auto reload to 20000
TIM3->CCER    |= 0x01;                              //set timer to output
TIM3->CCMR1     |= 0x68;                                //Set PWM mode 1 = 01101000


//timer 3 now set to 50hz

RCC->AHB1ENR        |= 0x05;                        //IO Port A and C clock enable  = 00000101

GPIOC->MODER        |= 0x400;                   //set PC6 as alternate function = 0000 0100 0000 0000
GPIOC->AFR[0]      = 0x02000000;            //Set AF to timer 3 = 0000 0010 0000 0000 0000 0000 0000 0000
GPIOC->OTYPER    = 0;                           //Set output as Push-Pull mode
GPIOC->OSPEEDR   = 0;                           //Set output speed 2MHz low speed
GPIOC->PUPDR       = 0;                             //Set no pull up and pull down

GPIOA->MODER        &= 0xfffffffc;          // Set Port a Bit 0 Active input
GPIOA->OTYPER    = 0;                           //Set output as Push-Pull mode
GPIOA->OSPEEDR   = 0;                           //Set output speed 2MHz low speed
GPIOA->PUPDR       = 0;                             //Set no pull up and pull down




while(1)
    {
            TIM2->CCR1 |= 0x28A;            //650us pulses
            delay();
            TIM2->CCR1 |= 0x73A;                //1850us pulses
            delay();
    }
}

Answer 1

It's pretty normal if you configure TIM3 but modify TIM2 ...

TIM3->CR1       |= 0x81;
...
TIM2->CCR1 |= 0x28A;

Answer 2

You have configured the output to channel 2 of Timer 3 by setting the value:

TIM3->CCER    |= 0x01; 

for this value of CCER register, the PWM outptut will be on pin PB8 .

To get the output on pin PC6 , set the value:

TIM3->CCER |= 0x1000;

and also, according to the documentation, channel 1 of TIM3 is connected to pins PA6, PB4, PC6. Check for PWM output on these three pins.