/* p5_5.c Toggle LED0 on SAMD21 Xplained Pro using TC5
 *
 * This program uses TC5 to create a delay function that delays
 * the multiple of milliseconds.
 *
 * TC5 is configured to run continuously in 8-bit mode. TC5 counter 
 * clock is derived from 1 MHz main clock. The prescaler divides the
 * GCLK_TC5 by 4. The TOP count is set to 250-1. The counter
 * overflows at 1 MHz / 4 / 250 = 1 kHz.
 * The main function calls the delay for 1000 loops between each
 * toggle of the LED0. 1000 delay loops of 1 ms gives 1 second delay.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

void delayMs(int n);

int main (void) {
    REG_GCLK_CLKCTRL = 0x401C;      /* GCLK0 -> TC4/TC5 */
    REG_PM_APBCMASK |= 0x00002000;  /* enable TC5 Clock in PM */
    REG_TC5_CTRLA = 1;              /* reset TC5 before configuration */
    while (REG_TC5_CTRLA & 1) {}    /* wait till out of reset */
    REG_TC5_CTRLA = 0x0204;         /* prescaler /4, 8-bit mode, NFRQ */
    REG_TC5_COUNT8_PER = 250 - 1;   /* TOP count value in 8-bit mode */
    REG_PORT_DIR1 |= 0x40000000;    /* make PB30 output */

    while(1) {
        REG_PORT_OUT1 ^= 0x40000000; /* toggle LED0 */
        delayMs(1000);              /* make a 1 second delay */
    }
}

/* delay number of milliseconds */
void delayMs(int n) {
    REG_TC5_COUNT8_COUNT = 0;       /* start the first count from 0 */
    REG_TC5_INTFLAG = 1;            /* clear OVF flag */
    REG_TC5_CTRLA |= 2;             /* enable TC5 */
    for (; n > 0; n--) {
        while ((REG_TC5_INTFLAG & 1) == 0) {}  /* wait until OVF is set */
        REG_TC5_INTFLAG = 1;        /* clear OVF flag */
    }
    REG_TC5_CTRLA &= ~2;            /* disable TC5 */
}