/* p11_1.c Using TIM3 for PWM Output
 *
 * This program configures TIM3 with prescaler divides by 5
 * so that the timer counter is counting at 1.6 MHz.
 * ARR register is loaded with 26666 and CCR1 is loaded with 8888.
 * The channel 1 is configured as PWM mode. The output of Ch1 is
 * turned on when the counter starts counting from 0. When the
 * counter matches the content of CCR1, Ch1 output is turned off.
 * When the counter matches ARR, the counter is cleared to 0 and
 * the output is turned on and the counter starts counting up again.
 * The output frequency is 1.6M / 26667 = 60Hz.
 * The LED will be on for 8889/26667 = 33% of the time.
 * The output pin of TIM3 Ch1 is PA6 and the alternate function
 * of PA6 should be set to AF1.
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0.
 */

#include "stm32f0xx.h"

int main(void) {
    RCC->AHBENR |=  0x00020000;     /* enable GPIOA clock */
    GPIOA->AFR[0] |= 0x01000000;    /* PA6 pin for TIM3 channel 1 */
    GPIOA->MODER &= ~0x00003000;
    GPIOA->MODER |=  0x00002000;

    /* setup TIM3 */
    RCC->APB1ENR |= 0x00000002;     /* enable TIM3 clock */
    TIM3->PSC = 5 - 1;              /* divided by 5 */
    TIM3->ARR = 26667 - 1;          /* divided by 26667 */
    TIM3->CNT = 0;
    TIM3->CCMR1 = 0x0060;           /* PWM mode */
    TIM3->CCER = 1;                 /* enable PWM Ch1 */
    TIM3->CCR1 = 8889;              /* pulse width 1/3 of the period */
    TIM3->CR1 = 1;                  /* enable timer */

    while(1) {
    }
}