/* p11_2.c Using TIM8 for PWM Output
 *
 * This program configures TIM8 with prescaler divides by 10
 * 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 Ch1N is
 * turned on when the counter starts counting from 0. When the 
 * counter matches the content of CCR1, Ch1N 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 LED will be on for 8889/26667 = 30% of the time.
 * The output pin of TIM8 Ch1N is PA5 and the alternate function
 * of PA5 should be set to AF1.
 *
 * This program is similar to p11_1.c except:
 * 1. Each PWM output channel (Chx) has a complementary output (ChxN)
 *    and we are using the Ch1N output.
 * 2. The output needs to be enabled at TIM8_BDTR register.
 * 
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0
 */
 
#include "stm32f4xx.h"

int main(void) {
    RCC->AHB1ENR |= 1;              /* enable GPIOA clock */
    
    GPIOA->AFR[0] |= 0x00300000;    /* PA5 pin for TIM8 */
    GPIOA->MODER &= ~0x00000C00;
    GPIOA->MODER |=  0x00000800;
    
    /* setup TIM8 */
    RCC->APB2ENR |= 2;              /* enable TIM8 clock */
    TIM8->PSC = 10 - 1;             /* divided by 10 */
    TIM8->ARR = 26667 - 1;          /* divided by 26667 */
    TIM8->CNT = 0;
    TIM8->CCMR1 = 0x0060;           /* PWM mode */
    TIM8->CCER = 4;                 /* enable PWM Ch1N */
    TIM8->CCR1 = 8889 - 1;          /* pulse width 1/3 of the period */
    TIM8->BDTR |= 0x8000;           /* enable output */
    TIM8->CR1 = 1;                  /* enable timer */

    while(1) {
    }
}