/* p5_8.c TIM3 Measuring Period and Frequency

 * This program configures TIM2 CH1 to toggle PA5 as was done in p5_6.
 * The TIM3 CH1 is set to do Input Capture from PA6. The program waits
 * for capture flag (CC1IF) to set then calculates the period and 
 * frequency of the input signal.
 * A jumper should be used to connect PA5 to PA6.
 * 
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0
 */
#include "stm32f4xx.h"

int period;
float frequency;

int main(void) {
    int last = 0;
    int current;
    
    // configure PA5 as output of TIM2 CH1
    RCC->AHB1ENR |=  1;             /* enable GPIOA clock */
    GPIOA->MODER &= ~0x00000C00;    /* clear pin mode */
    GPIOA->MODER |=  0x00000800;    /* set pin to alternate function */
    GPIOA->AFR[0] &= ~0x00F00000;   /* clear pin AF bits */
    GPIOA->AFR[0] |= 0x00100000;    /* set pin to AF1 for TIM2 CH1 */
    
    // configure TIM2 to wrap around at 1 Hz 
	// and toggle CH1 output when the counter value is 0
    RCC->APB1ENR |= 1;              /* enable TIM2 clock */
    TIM2->PSC = 1600 - 1;           /* divided by 1600 */
    TIM2->ARR = 3000 - 1;           /* divided by 3000 */
    TIM2->CCMR1 = 0x30;             /* set output to toggle on match */
    TIM2->CCR1 = 0;                 /* set match value */
    TIM2->CCER |= 1;                /* enable ch 1 compare mode */
    TIM2->CNT = 0;                  /* clear counter */
    TIM2->CR1 = 1;                  /* enable TIM2 */
        
    // configure PA6 as input of TIM3 CH1
    RCC->AHB1ENR |=  1;             /* enable GPIOA clock */
    GPIOA->MODER &= ~0x00003000;    /* clear pin mode */
    GPIOA->MODER |=  0x00002000;    /* set pin to alternate function */
    GPIOA->AFR[0] &= ~0x0F000000;   /* clear pin AF bits */
    GPIOA->AFR[0] |= 0x02000000;    /* set pin to AF2 for TIM3 CH1 */

    // configure TIM3 to do input capture with prescaler ...
    RCC->APB1ENR |= 2;              /* enable TIM3 clock */
    TIM3->PSC = 16000 - 1;          /* divided by 16000 */
    TIM3->CCMR1 = 0x41;             /* set CH1 to capture at every edge */
    TIM3->CCER = 0x0B;              /* enable CH 1 capture both edges */
    TIM3->CR1 = 1;                  /* enable TIM3 */

    while (1) {
        while (!(TIM3->SR & 2)) {}  /* wait until input edge is captured */
        current = TIM3->CCR1;       /* read captured counter value */
        period = current - last;    /* calculate the period */
        last = current;
        frequency = 1000.0f / period;
        last = current;
    }
}