/* p11_5.c Comparison between edge-aligned and center-aligned PWM
 *
 * In this program, TIM8 Ch1 is configured as center-aligned PWM with
 * output on PC6 pin and TIM2 Ch1 is configured as edge-aligned PWM
 * with output on PA5 pin for comparison.
 *
 * You will find two differences between these two PWM generation:
 * 1. For edge-aligned PWM, the counter counts from 0 to the value
 *    of ARR then it takes one clock cycle to reset to 0. So to
 *    count 1000 clock cycles, the ARR should be loaded with 999.
 *    For center-aligned PWM, the counter counts up from 0 to the
 *    value of ARR then immediately counts down back to 0. So to
 *    count 1000 clock cycles, the ARR should be loaded with 1000.
 * 2. For edge-aligned PWM, each output cycle the counter counts 
 *    from 0 to the value of ARR. For center-aligned PWM, each
 *    output cycle, the counter counts from 0 up to the value of
 *    ARR then back down to 0. For the same value of ARR, the 
 *    center-aligned PWM takes twice as long as edge-aligned PWM
 *    to complete an output cycle.
 * 
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0
 */
 
#include "stm32f4xx.h"

void TIM8_center_aligned(void);
void TIM2_edge_aligned(void);

int main(void) {
    TIM8_center_aligned();
    TIM2_edge_aligned();
    
    while(1) {
    }
}

void TIM8_center_aligned(void) {
    RCC->AHB1ENR |= 4;              /* enable GPIOC clock */
    
    GPIOC->AFR[0] |= 0x03000000;    /* PC6 pin for tim8 Ch1 */
    GPIOC->MODER &= ~0x00003000;
    GPIOC->MODER |=  0x00002000;
    
    /* setup TIM8 */
    RCC->APB2ENR |= 2;              /* enable TIM8 clock */
    TIM8->PSC = 16 - 1;             /* divided by 16 */
    TIM8->ARR = 1000;               /* divided by 1000 */
    TIM8->CNT = 0;
    TIM8->CCMR1 = 0x0060;           /* PWM mode */
    TIM8->CCER = 1;                 /* enable PWM Ch1 */
    TIM8->CCR1 = 300 - 1;           /* pulse width 300 */
    TIM8->BDTR |= 0x8000;           /* enable output */
    TIM8->CR1 = 0x21;               /* center-aligned, enable timer */
}

void TIM2_edge_aligned(void) {
    RCC->AHB1ENR |= 1;              /* enable GPIOA clock */
    
    GPIOA->AFR[0] |= 0x00100000;    /* PA5 pin for tim2 */
    GPIOA->MODER &= ~0x00000C00;
    GPIOA->MODER |=  0x00000800;
    
    /* setup TIM2 */
    RCC->APB1ENR |= 1;              /* enable TIM2 clock */
    TIM2->PSC = 16 - 1;             /* divided by 16 */
    TIM2->ARR = 1000 - 1;           /* divided by 1000 */
    TIM2->CNT = 0;
    TIM2->CCMR1 = 0x0060;           /* PWM mode */
    TIM2->CCER = 1;                 /* enable PWM Ch1 */
    TIM2->CCR1 = 300 - 1;           /* pulse width 300 */
    TIM2->CR1 = 1;                  /* edge-aligned enable timer */
}