====== T03 - Stopwatch ======

Write a program for [[courses:be2m37mam:hardware:nucleo|Nucleo STM32F401RE]] and [[courses:be2m37mam:hardware:shield|Experimental shield]], that performs a 1s precision stopwatch (or better).

===== Instructions: =====

  * Use LED display on the Experimental shield
  * Use button S1 to start/stop/clear stopwatch

==== How timer / counter works ====

{{ :courses:be2m37mam:tasks:timer-1.svg |}}

==== Timer TIM2 (pooling) ====

<code c>
#include "stm32f4xx.h"

#define setbit(reg, bit)      ((reg) |= (1U << (bit)))
#define clearbit(reg, bit)    ((reg) &= (~(1U << (bit))))
#define togglebit(reg, bit)   ((reg) ^= (1U << (bit)))
#define getbit(reg, bit)      (((reg) & (1U << (bit))) >> (bit))

void initLED(void) {
    setbit(RCC->AHB1ENR, 0);
    setbit(GPIOA->MODER, 10);
}

void initTIM2(void)
{
    /*
     * TIM2 je pripojen ke sbernici APB1, ktera bezi na 16MHz
     * frekvence pred TIM2 je zvojnasobena PLL
     */
    setbit(RCC->APB1ENR, 0);  /* enable Clock for TIM2 */
    TIM2->PSC = ?;                /* prescaler - doplnte podle potreby */
    TIM2->ARR = ?;                /* autoreload - doplnte podle potreby */
    setbit(TIM2->CR1, 0);        /* enable TIM2 */
    clearbit(TIM2->SR, 0);       /* status TIM2 */
}

int main(void)
{
    initLED();
    initTIM2();

    while(1)
    {
        /* test na UEV (update event)    */
        if(getbit(TIM2->SR, 0))
        {
            togglebit(GPIOA->ODR, 5);
            /* vraceni status bitu na log 0 */
            clearbit(TIM2->SR, 0);
        }
    }
}
</code>