/* p11_5.c Comparison between edge-aligned and center-aligned PWM
 *
 * In this program, TIM16 Ch1 is configured as edge-aligned PWM with
 * output on PB8 pin and TIM3 Ch1 is configured as center-aligned PWM
 * with output on PA6 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 500.
 * 2. The output of PWM is active when the counter value is below
 *    the value of CCRx register. For edge-aligned PWM, the output
 *    is active counting up from 0 and turned off when it reaches
 *    the value of CCRx. For an output pulse of 300 clock cycles,
 *    300 is loaded in the CCRx register. For center-aligned PWM,
 *    the output is active when counting down below the value of 
 *    CCRx until it is counting up to the value of CCRx. For an
 *    output of 300 cycles, 150 should be loaded in the CCRx.
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0.
 */
 
#include "stm32f0xx.h"

void TIM16_edge_aligned(void);
void TIM3_center_aligned(void);

int main(void) {
    TIM16_edge_aligned();
    TIM3_center_aligned();

    while(1) {
    }
}

void TIM16_edge_aligned(void) {
    RCC->AHBENR |=  0x00040000;     /* enable GPIOB clock */
    GPIOB->AFR[1] |= 0x00000002;    /* PB8 pin for TIM16 channel N1 */
    GPIOB->MODER &= ~0x00030000;
    GPIOB->MODER |=  0x00020000;
    
    /* setup TIM16 */
    RCC->APB2ENR |= 0x00020000;     /* enable TIM16 clock */
    TIM16->PSC = 8 - 1;             /* divided by 8 */
    TIM16->ARR = 1000 - 1;          /* divided by 2000 */
    TIM16->CNT = 0;
    TIM16->CCMR1 = 0x0060;          /* PWM mode */
    TIM16->CCER = 1;                /* enable PWM Ch1 */
    TIM16->CCR1 = 300;              /* pulse width 300 */
    TIM16->BDTR |= 0x8000;          /* enable output */
    TIM16->CR1 = 0x01;              /* edge-aligned enable timer */
}

void TIM3_center_aligned(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 = 8 - 1;              /* divided by 8 */
    TIM3->ARR = 500;                /* divided by 1000 */
    TIM3->CNT = 0;
    TIM3->CCMR1 = 0x0060;           /* PWM mode */
    TIM3->CCER = 1;                 /* enable PWM Ch1 */
    TIM3->CCR1 = 150;               /* pulse width 300 */
    TIM3->CR1 = 0x21;               /* center-aligned, enable timer */
}