/* p5_6.c Toggle PWM/D9 PIN using TIM3 Compare mode
 *
 * This program configures TIM3 with prescaler divides by 800
 * and counter wraps around at 10000. So the 8 MHz system clock
 * is divided by 1600 then divided by 10000 to become 1 Hz.
 * The channel 1 is configured for compare mode to toggle the output
 * pin every time the timer counter matches the CCR2 register.
 * The output pin of TIM3 CH2 is PC7 (PWM/D9) and the alternate function
 * of PC7 should be set to AF0.
 * 
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */
#include "stm32f0xx.h"
int main(void) {
    // configure PC7 as output
    RCC->AHBENR |=   0x00080000;    /* enable GPIOC clock */
    GPIOC->MODER &= ~0x0000C000;    /* clear pin mode */
    GPIOC->MODER |=  0x00008000;    /* set pin to alternate function */
    GPIOC->AFR[0] &= 0xF0000000;    /* clear pin AF bits to set pin to AF0 for TIM3 CH2 */
// configure TIM3 to wrap around at 1 Hz 
	// and toggle CH1 output when the counter value is 0
    RCC->APB1ENR |= 0x00000002;     /* enable TIM3 clock */
    TIM3->PSC = 800 - 1;            /* divided by 800 */
    TIM3->ARR = 10000 - 1;          /* divided by 10000 */
    TIM3->CCMR1 = 0x3000;           /* set output to toggle on match */
TIM3->CCR2 = 0;                 /* set match value */
    TIM3->CCER |= 0x10;             /* enable CH2 compare mode */
    TIM3->CNT = 0;                  /* clear counter */
    TIM3->CR1 = 1;                  /* enable TIM3 */
while (1) {
    }
}