/* p6_8.c Demonstrate Nested Interrupts
 *
 * TC6 is setup to interrupt at about 1 Hz. In the interrupt handler,
 * PA16 is turned on and a delay function of 500 ms is called.
 * PA16 is turned off at the end of the delay.
 *
 * TC7 is setup to interrupt at about 10 Hz. In the interrupt handler,
 * PA17 and the LED0 is turned on and a delay function of 25 ms is called.
 * PA17 and the LED0 is turned off at the end of the delay.
 *
 * When TC6 has the higher priority (the way this code is), the TC7
 * interrupts are blocked by TC6 interrupt handler and the LED stops
 * blinking intermittently. You can see their interactions better
 * with an oscilloscope on PA16 and PA17.
 *
 * When TC7 has the higher priority (you need to switch the priority of
 * the two timers at the #defines), the TC6 interrupt handler is
 * preempted by TC7 interrupts and the LED is blinking all the time.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

void delayMs(int n);

/* priority of Timer1 and Timer2 should be between 0 and 3 */
#define PRIO_TC6 2
#define PRIO_TC7 3

int main (void) {
    __disable_irq();
    REG_GCLK_CLKCTRL = 0x401D;      /* GCLK0 -> TC6/TC7 */
    REG_PM_APBCMASK |= 0x0000C000;  /* enable TC7/6 Clock in PM */

    REG_TC6_CTRLA = 1;              /* reset TC6 before configuration */
    while (REG_TC6_CTRLA & 1) {}    /* wait till out of reset */
    REG_TC6_CTRLA = 0x0520;         /* prescaler /64, 16-bit mode, MFRQ */
    REG_TC6_COUNT16_CC0 = 15500;    /* set TOP count in MFRQ */
    REG_TC6_CTRLA |= 2;             /* enable TC6 */
    REG_TC6_INTENSET = 0x10;        /* enable match interrupt */
    NVIC_SetPriority(TC6_IRQn, PRIO_TC6);
    NVIC_EnableIRQ(TC6_IRQn);       /* enable TC6 interrupt in NVIC */

    REG_TC7_CTRLA = 1;              /* reset TC7 before configuration */
    while (REG_TC7_CTRLA & 1) {}    /* wait till out of reset */
    REG_TC7_CTRLA = 0x0520;         /* prescaler /64, 16-bit mode, MFRQ */
    REG_TC7_COUNT16_CC0 = 1562;     /* set TOP count in MFRQ */
    REG_TC7_CTRLA |= 2;             /* enable TC7 */
    REG_TC7_INTENSET = 0x10;        /* enable match interrupt */
    NVIC_SetPriority(TC7_IRQn, PRIO_TC7);
    NVIC_EnableIRQ(TC7_IRQn);       /* enable TC7 interrupt in NVIC */

    __enable_irq();                 /* enable interrupt globally */

    REG_PORT_DIRSET0 = 0x00030000;  /* make PA16/PA17 output */
    REG_PORT_OUTCLR0 = 0x00030000;  /* turn off PA16/PA17 */
    REG_PORT_DIRSET1 = 0x40000000;  /* make PB30 output */

    while(1) {
    }
}

void TC6_Handler(void) {
    REG_PORT_OUTSET0 = 0x00010000;  /* turn on PA16 */
    delayMs(500);
    REG_PORT_OUTCLR0 = 0x00010000;  /* turn off PA16 */
    REG_TC6_INTFLAG = 0x10;         /* clear MC0 flag */
}

void TC7_Handler(void) {
    REG_PORT_OUTSET0 = 0x00020000;  /* turn on PA17 */
    REG_PORT_OUTCLR1 = 0x40000000;  /* turn on LED0 */
    delayMs(25);
    REG_PORT_OUTCLR0 = 0x00020000;  /* turn off PA17 */
    REG_PORT_OUTSET1 = 0x40000000;  /* turn off LED0 */
    REG_TC7_INTFLAG = 0x10;         /* clear MC0 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");
}