/* p5_7.c Toggle LED0 on SAMD21 Xplained Pro using TC7
 *
 * This program uses TC7 to blink the LED0 in 16-bit mode.
 *
 * TC7 is configured to run continuously in 16-bit mode. TC7 counter 
 * clock is derived from 1 MHz main clock. The prescaler divides the
 * GCLK_TC7 by 16. The TOP count is set at 31,250-1 in Match Frequency
 * operation. The counter overflows at 1 MHz / 16 / 31250 = 2.0 Hz.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

int main (void) {
    REG_GCLK_CLKCTRL = 0x401D;      /* GCLK0 -> TC6/TC7 */
    REG_PM_APBCMASK |= 0x00008000;  /* enable TC7 Clock in PM */
    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 = 31250 - 1; /* set TOP count in MFRQ */
    REG_TC7_CTRLA |= 2;             /* enable TC7 */
    REG_PORT_DIR1 |= 0x40000000;    /* make PB30 output */

    while(1) {
        if (REG_TC7_INTFLAG & 1) {  /* wait until OVF is set */
            REG_TC7_INTFLAG = 1;    /* clear OVF flag */
            REG_PORT_OUT1 ^= 0x40000000;    /* toggle LED0 */
        }
    }
}