/* p5_8.c TIM3 Measuring Period and Frequency
	
 * This program configures TIM14 CH1 to toggle PA7 (PWM/D11)
 * The TIM3 CH1 is set to do Input Capture from PB4 (D5). 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 PA7 (D11) to PB4 (D5).
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */
#include "stm32f0xx.h"
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unsigned short period[8];
float frequency[8];
int i;

int main(void) {
    unsigned short last = 0;
    unsigned short current;

    // configure PA7 as output of TIM14 CH1
    RCC->AHBENR |=  0X00020000; /* enable GPIOA clock */
    GPIOA->MODER &= ~0x0000C000;        /* clear pin mode */
    GPIOA->MODER |=  0x00008000;        /* set pin to alternate function */
    GPIOA->AFR[0] &= ~0xF0000000;       /* clear pin AF bits */
    GPIOA->AFR[0] |=  0x40000000;       /* set pin to AF1 for TIM14 CH1 */

    // configure TIM14 to wrap around at 3.33 Hz
	// and toggle CH1 output when the counter value is 0
    RCC->APB1ENR |= 0x00000100;         /* enable TIM14 clock */
    TIM14->PSC = 800 - 1;               /* divided by 800 */
    TIM14->ARR = 3000 - 1;              /* divided by 3000 */
    TIM14->CCMR1 = 0x30;                /* set output to toggle on match */
    TIM14->CCR1 = 0;                    /* set match value */
    TIM14->CCER |= 1;                   /* enable ch 1 compare mode */
    TIM14->CNT = 0;                     /* clear counter */
    TIM14->CR1 = 1;                     /* enable TIM14 */

    // configure PB4 as input of TIM3 CH1
    RCC->AHBENR |=  0x00040000;         /* enable GPIOB clock */
    GPIOB->MODER &= ~0x00000300;        /* clear pin mode */
    GPIOB->MODER |=  0x00000200;        /* set pin to alternate function */
    GPIOB->AFR[0] &= ~0x000F0000;       /* clear pin AF bits */
    GPIOB->AFR[0] |=  0x00010000;       /* set pin to AF1 for TIM3 CH1 */

    // configure TIM3 to do input capture with prescaler ...
    RCC->APB1ENR |= 0x00000002;         /* enable TIM3 clock */
    TIM3->PSC = 8000 - 1;               /* divided by 8000 */
    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) {
        for (i = 0; i < 8; i++)
        {
            while (!(TIM3->SR & 0x2)) {}    /* wait until input edge is captured */
            current = TIM3->CCR1;           /* read captured counter value */
            period[i] = current - last;     /* calculate the period */
            last = current;
            frequency[i] = 1000.0f / period[i];
        }
        __NOP();	/* for setting breakpoint after 8 iterations */
    }
}