====== 5. Časovače ======

===== Nastavení časovače - PWM =====

Referenční manuál, str. 331.

<code c>
#define PWMPERIOD 100
#define SAMPLE 100

void TIM4_IRQHandler(void)
{
    static uint32_t t = 0;
    static uint16_t duty = 0;

    // clear interrupt status
    if (TIM4->DIER & 0x01) {
        if (TIM4->SR & 0x01) {
            TIM4->SR &= ~(1U << 0);
        }
    }

    duty =(uint16_t)(PWMPERIOD/2.0 * (sin(2*M_PI*(double)t/(SAMPLE)) + 1.0));
    ++t;
    if (t == SAMPLE) t = 0;
    // set new duty cycle
    TIM4->CCR1 = duty;
}

int main(void)
{
    // enable GPIOB clock and set alternate function
    RCC->AHB1ENR |= (1 << 1);
    GPIOB->MODER |= (0x2 << 12);   // pin 6 af mode 10
    // Choose Timer4 as Alternative Function for pin 12
    GPIOB->AFR[1] |= (0x2 << 24);
    
    // enable TIM4 clock (bit2)
    RCC->APB1ENR |= (1 << 2);

    // fCK_PSC / (PSC[15:0] + 1)
    // 84 Mhz / 8399 + 1 = 10 khz timer clock speed
    TIM4->PSC = 8399;
    // set period
    TIM4->ARR = PWMPERIOD;
    // set duty cycle on channel 1
    TIM4->CCR1 = 1;

    // enable channel 1 in capture/compare register
    // set oc1 mode as pwm (0b110 or 0x6 in bits 6-4)
    TIM4->CCMR1 |= (0x6 << 4);
    // enable oc1 preload bit 3
    TIM4->CCMR1 |= (1 << 3);
    // enable capture/compare ch1 output
    TIM4->CCER |= (1 << 0);
    // enable update interrupt
    TIM4->DIER |= (1 << 0);

    NVIC_SetPriority(TIM4_IRQn, 2); // Priority level 2
    // enable TIM4 IRQ from NVIC
    NVIC_EnableIRQ(TIM4_IRQn);

    // Enable Timer 4 module (CEN, bit0)
    TIM4->CR1 |= (1 << 0);

    while(1)
    {
        // Do nothing.
    }

    return 0;
}
</code>