/* p6_7.c Toggle LED0 using TC6 and TC7 Match Interrupts
 *
 * TC6 and 7 are configured to run continuously in 16-bit mode. TC6/7 
 * counter clock is derived from 1 MHz main clock. The prescaler divides the
 * GCLK by 16. The TOP count is set at 31,250-1 for TC6 and 30,000-1 for TC7
 * in Match Frequency operation. 
 * The counter overflows at 1 MHz / 16 / 31,250 = 2.0 Hz for TC6 and
 * 1 MHz / 16 / 30,000 = 2.08 Hz for TC7.
 *
 * Everytime the counter matches the CC register, an interrupt is triggered. 
 * In the interrupt handler, PB30 is turned on by TC6 and turned off by TC7.
 * The yellow LED0 on board is connected to PB30. It is on from TC6
 * interrupt to TC7 interrupt and off from TC7 interrupt to TC6 interrupt.
 * Because these two interrupts have different frequency, the on time of the
 * LED0 changes.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

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 = 0x0420;         /* prescaler /16, 16-bit mode, MFRQ */
    REG_TC6_COUNT16_CC0 = 31250 - 1; /* set TOP count in MFRQ */
    REG_TC6_CTRLA |= 2;             /* enable TC6 */
    REG_TC6_INTENSET = 0x10;        /* enable match interrupt */
    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 = 0x0420;         /* prescaler /16, 16-bit mode, MFRQ */
    REG_TC7_COUNT16_CC0 = 30000 - 1; /* set TOP count in MFRQ */
    REG_TC7_CTRLA |= 2;             /* enable TC7 */
    REG_TC7_INTENSET = 0x10;        /* enable match interrupt */
    NVIC_EnableIRQ(TC7_IRQn);       /* enable TC7 interrupt in NVIC */

    __enable_irq();                 /* enable interrupt globally */

    REG_PORT_DIRSET1 = 0x40000000;  /* make PB30 output */

    while(1) {
    }
}

void TC6_Handler(void) {
    REG_PORT_OUTCLR1 = 0x40000000;  /* turn on LED0 */
    REG_TC6_INTFLAG = 0x10;         /* clear MC0 flag */
}

void TC7_Handler(void) {
    REG_PORT_OUTSET1 = 0x40000000;  /* turn off LED0 */
    REG_TC7_INTFLAG = 0x10;         /* clear MC0 flag */
}