/* p6_1.c using SW0 interrupt
 *
 * User Switch SW0 is used to generate interrupt through PA15.
 * When the switch is pressed, PA15 is shorted to ground through a
 * resistor. In this program, PA15 is configured as input with 
 * internal pull-up resistor. So the pin idles at 1 and becomes 0
 * when switch is pressed.
 * The falling-edge of PA15 (when switch is pressed) triggers an
 * interrupt from External Interrupt Controller (EIC).
 * In the interrupt handler, the user LED0 is blinked twice.
 * It serves as a crude way to debounce the switch.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a 
 */

#include "samd21.h"

unsigned char* ARRAY_PORT_PINCFG0 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX0 = (unsigned char*)&REG_PORT_PMUX0;

void delayMs(int n);

int main (void) {
    __disable_irq();
    REG_PORT_DIRSET1 = 1 << 30;     /* make PB30 output for LED */
    
    ARRAY_PORT_PINCFG0[15] |= 5;    /* make PA15 EXTINT15 */
    ARRAY_PORT_PMUX0[7] = 0;        /* PA15 = EXTINT15 */
    REG_PORT_OUTSET0 = 1 << 15;

    REG_GCLK_CLKCTRL = 0x4005;      /* GCLK0 -> EIC */
    REG_EIC_CONFIG1 |= 0xA0000000;  /* EXTINT15 filtered falling-edge */
    REG_EIC_INTENSET = 0x8000;      /* enable EXTINT15 */
    REG_EIC_CTRL = 2;               /* enable EIC */
    NVIC_EnableIRQ(EIC_IRQn);
    __enable_irq();

    while(1) {
    }
}

/* in the interrupt handler, the yellow LED0 blinks twice */
void EIC_Handler(void) {
    if (REG_EIC_INTFLAG & 0x8000) {
        REG_PORT_OUTCLR1 = 0x40000000; /* turn on LED */
        delayMs(250);
        REG_PORT_OUTSET1 = 0x40000000; /* turn off LED */
        delayMs(250);
        REG_PORT_OUTCLR1 = 0x40000000; /* turn on LED */
        delayMs(250);        
        REG_PORT_OUTSET1 = 0x40000000; /* turn off LED */
        delayMs(250);
        REG_EIC_INTFLAG = 0x8000;   /* clear interrupt flag */
    } else {
        /* spurious interrupt?, clear all interrupt flags */
        REG_EIC_INTFLAG = REG_EIC_INTFLAG; /* clear all EIC interrupt flags */
    }
}

/* millisecond delay based on 1 MHz system clock */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 199; i++)
            __asm("nop");
}