/* p6_3.c Non-maskable interrupt from PA08
 *
 * PA08 is configured to generate non-maskable interrupt.
 * In the interrupt handler, the user LED0 is blinked twice.
 *
 * 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) {
    REG_PORT_DIRSET1 = 0x40000000;  /* make PB30 output for LED */
    
    ARRAY_PORT_PINCFG0[8] |= 7;     /* make PA08 NMI */
    ARRAY_PORT_PMUX0[4] = 0;        /* PA08 = NMI */
    REG_PORT_DIRCLR0 = 0x0010;      /* PA08 input */
    REG_PORT_OUTSET0 = 0x0010;      /* pull up PA08 */

    REG_GCLK_CLKCTRL = 0x4005;      /* GCLK0 -> EIC */
    REG_EIC_NMICTRL |= 0xA;         /* NMI filtered falling-edge */

    while(1) {
    }
}

/* in the interrupt handler, the yellow LED0 blinks twice */
void NMI_Handler(void) {
        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_NMIFLAG = 1;   /* clear interrupt flag */
}

/* 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");
}