/* p11_4.c  Variable duty cycle PWM to control LED on duration
 *
 * This program uses TCC0 to generate periodic waveform outputs.
 * The program is based on p11_3.c with one change:
 * The prescaler is configured to divide the clock by 16 to
 * slow down the frequency so that the output change is
 * visible by the naked eyes.
 *
 * PB30 is used for TCC0 output channel 0 (TCC0/WO[0]), which
 * is connected to the on-board LED0. You may observe the change
 * of the duration the light is on because of the change of 
 * duty cycle.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

void delayMs(int n);

unsigned char* ARRAY_PORT_PINCFG1 = (unsigned char*)&REG_PORT_PINCFG1;
unsigned char* ARRAY_PORT_PMUX1 = (unsigned char*)&REG_PORT_PMUX1;

int main (void) {
    REG_GCLK_CLKCTRL = 0x401A;      /* GCLK0 -> TCC0, TCC1 */
    REG_PM_APBCMASK |= 0x00000100;  /* enable TCC0 Clock in PM */
    REG_TCC0_CTRLA = 1;             /* reset */
    while (REG_TCC0_CTRLA & 1) {}   /* wait till out of reset */
    REG_TCC0_CTRLA |= 0x00000400;   /* prescaler divided by 16 */
    REG_TCC0_WAVE = 2;              /* Normal PWM */
    REG_TCC0_PER = 16666 - 1;       /* period */
    REG_TCC0_CC0 = 1000;            /* pulse width */
    REG_TCC0_DRVCTRL |= 0x00010000; /* invert ch0 output */
    REG_TCC0_CTRLA |= 2;            /* enable */

    ARRAY_PORT_PINCFG1[30] |= 1;    /* make PB30 output for TCC0 */
    ARRAY_PORT_PMUX1[15] = 0x04;    /* PB30 = TCC0/WO[0] */
        
    while(1) {
        REG_TCC0_CC0 = REG_TCC0_CC0 * 110 / 100;
        if (REG_TCC0_CC0 > 16665)    /* wrap around when reaches 100% */
            REG_TCC0_CC0 = 1000;
        delayMs(400);
    }
}

/* 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");
}