/* p6_6.c Timer TIM3 interrupt
 *
 * Timer TIM3 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 timer is set up for output compare interrupt for channel 2. When the
 * counter matches the CCR2 register, the output toggles and an interrupt
 * is triggered. In the interrupt handler, the PERIOR value is added CCR2
 * so that the next CCR2 match occurs after the PERIOR count.
 * When the PERIOD is set to 1000, the output toggles at 1 Hz.
 * The output of TIM3 Channel 1 is PC7 (PWM/D9).
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */
#include "stm32f0xx.h"

#define PERIOD 1000
void delayMs(int n);

int main(void)
{
	__disable_irq();            /* global disable IRQs */

	// Configure PC7 as TIM3_CH2 output to drive the LED
	RCC->AHBENR |=   0x00080000;            /* enable GPIOC clock */
	GPIOC->MODER &= ~0x0000C000;            /* clear pin mode */
	GPIOC->MODER |=  0x00008000;            /* set pin to alternate function */
	GPIOC->AFR[0] &= 0xF0000000;            /* clear pin AF bits to set pin to AF0 for TIM3 CH2 */


	// configure TIM3 to wrap around at 1 Hz
	// and toggle CH2 output when the counter value is 0
	RCC->APB1ENR |= 0x00000002;             /* enable TIM3 clock */
	TIM3->PSC = 8000 - 1;                   /* divided by 8000 */
	TIM3->ARR = 0xFFFF;                     /* set to max value */
	TIM3->CCMR1 = 0x3000;                   /* set output to toggle on match */
	TIM3->CCR2 = PERIOD;                    /* set match value */
	TIM3->CCER |= 0x10;                     /* enable CH2 compare mode */
	TIM3->CNT = 0;                          /* clear counter */
	TIM3->CR1 = 1;                          /* enable TIM3 */
	TIM3->SR = 0;                           /* clear UIF */
	TIM3->DIER |= 0x00000004;               /* enable CC2IE */
	NVIC_EnableIRQ(TIM3_IRQn);              /* enable interrupt in NVIC */

	__enable_irq();                         /* global enable IRQs */

	while (1) {
	}
}

void TIM3_IRQHandler(void)
{
	TIM3->SR = 0;                           /* clear UIF */
	TIM3->CCR2 = TIM3->CCR2 + PERIOD;       /* update CCR2 */
}