/* p6_2.c Interrupts from two input pins
 *
 * User Switches on PB10 and PC13 are used to generate interrupts.
 * PB10 is configured to generate interrupt. It has the 
 * pull-up resistor enabled. Use a jumper wire to ground the
 * pin to generate interrupts.
 * In the interrupt handler, the interrupt pending bits are
 * checked. If the interrupt is from PC13, the LED blinks twice.
 * If the interrupt is from PB10, the LED blinks three times.
 * The green LED (LD2) is connected to PA5.
 *
 * 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 */

    RCC->AHBENR |= 0x00080000;          /* enable GPIOC clock */
    RCC->AHBENR |= 0x00040000;          /* enable GPIOB clock */
    RCC->AHBENR |= 0x00020000;          /* enable GPIOA clock */
    RCC->APB2ENR |= 0x00000001;         /* enable SYSCFG clock */

    /* configure PA5 for LED */
    GPIOA->MODER &= ~0x00000C00;        /* clear pin mode */
    GPIOA->MODER |=  0x00000400;        /* set pin to output mode */

    /* configure PC13 for push button interrupt */
    GPIOC->MODER &= ~0x0C000000;        /* clear pin mode to input mode */
    
    SYSCFG->EXTICR[3] &= ~0x00F0;       /* clear port selection for EXTI13 */
    SYSCFG->EXTICR[3] |= 0x0020;        /* select port C for EXTI13 */
    
    EXTI->IMR  |= 0x2000;               /* unmask EXTI13 */
    EXTI->FTSR |= 0x2000;               /* select falling edge trigger */

    /* configure PB10 for interrupt */
    GPIOB->MODER &= ~0x00030000;        /* clear pin mode to input mode */
    GPIOB->PUPDR &= ~0x00300000;
    GPIOB->PUPDR |=  0x00100000;        /* enable pull up resistor */
    
    SYSCFG->EXTICR[2] &= ~0x0F00;       /* clear port selection for EXTI10 */
    SYSCFG->EXTICR[2] |= 0x0100;        /* select port B for EXTI10 */
    
    EXTI->IMR  |= 0x0400;               /* unmask EXTI10 */
    EXTI->FTSR |= 0x0400;               /* select falling edge trigger */

    NVIC_EnableIRQ(EXTI4_15_IRQn);     /* enable interrupt in NVIC */
    __enable_irq();                     /* global enable IRQs */
    
    while(1) {
    }
}

void EXTI4_15_IRQHandler(void) {
    if (EXTI->PR == 0x2000) {       /* interrupt from PC13 */
        GPIOA->BSRR = 0x00000020;   /* turn on green LED */
        delayMs(250);
        GPIOA->BSRR = 0x00200000;   /* turn off green LED */
        delayMs(250);
        GPIOA->BSRR = 0x00000020;   /* turn on green LED */
        delayMs(250);        
        GPIOA->BSRR = 0x00200000;   /* turn off green LED */
        delayMs(250);

        EXTI->PR = 0x2000;          /* clear interrupt pending flag */
    }
    else if (EXTI->PR == 0x0400) {  /* interrupt from PB10 */
        GPIOA->BSRR = 0x00000020;   /* turn on green LED */
        delayMs(250);
        GPIOA->BSRR = 0x00200000;   /* turn off green LED */
        delayMs(250);
        GPIOA->BSRR = 0x00000020;   /* turn on green LED */
        delayMs(250);        
        GPIOA->BSRR = 0x00200000;   /* turn off green LED */
        delayMs(250);
        GPIOA->BSRR = 0x00000020;   /* turn on green LED */
        delayMs(250);        
        GPIOA->BSRR = 0x00200000;   /* turn off green LED */
        delayMs(250);

        EXTI->PR = 0x0400;          /* clear interrupt pending flag */
    }
}

/* 8 MHz SYSCLK */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 1142; i++) ;
}