/* p6_5.c Timer TIM14 interrupt
 *
 * Timer TIM14 is configured as an up-counter. By default, the system clock is 
 * running at 8 MHz. The prescaler is set to divide by 8,000 that gives a
 * 1 kHz clock to the counter. The counter auto-reload is set to 999. When
 * the counter counts to 999, it updates the counter to zero and sets the
 * update interrupt flag (UIF). The UIE bit of TIM14->DIER is set so that 
 * the UIF triggers a timer interrupt. The interrupt frequency is 1 Hz.
 * In the timer interrupt handler, the green LED (PA5) is toggled and
 * the UIF is cleared.
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */
#include "stm32f0xx.h"

void delayMs(int n);

int main(void) {
    __disable_irq();                /* global disable IRQs */
	
    // configure PA5 as output to drive the LED
    RCC->AHBENR |=  0x00020000;     /* enable GPIOA clock */
    GPIOA->MODER &= ~0x00000C00;    /* clear pin mode */
    GPIOA->MODER |=  0x00000400;    /* set pin to output mode */
    
    // configure TIM14 to wrap around at 1 Hz
    RCC->APB1ENR |= 0x00000100;     /* enable TIM14 clock */
    TIM14->PSC = 8000 - 1;          /* divided by 8000 */
    TIM14->ARR = 1000 - 1;          /* divided by 1000 */
    TIM14->CNT = 0;                 /* clear timer counter */
    TIM14->CR1 = 1;                 /* enable TIM14 */

    TIM14->DIER |= 1;               /* enable UIE */
    NVIC_EnableIRQ(TIM14_IRQn);     /* enable interrupt in NVIC */
    
    __enable_irq();                 /* global enable IRQs */

    while(1) {
    }
}

void TIM14_IRQHandler(void) {
    TIM14->SR = 0;                  /* clear UIF */
    GPIOA->ODR ^= 0x20;             /* toggle LED */
}