/* p7_4.c: Use DAC to generate sawtooth waveform

 * The DAC is initialized with no buffer and use software trigger,
 * so every write to the DAC data register will change the analog output.
 * This program calculates a lookup table at the initialization to be used
 * to generate a sine wave output through a DAC.
 * The output of DAC is on pin PA02.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"
#include <math.h>

unsigned char* ARRAY_PORT_PINCFG0 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX0 = (unsigned char*)&REG_PORT_PMUX0;

#define WAVEFORM_LENGTH 256
int sinewave[WAVEFORM_LENGTH];

int main (void) {
    int i;
    double Radians;
    const double M_PI = 3.1415926535897;

    /* construct data table for a sine wave */
    Radians = 2 * M_PI / WAVEFORM_LENGTH;

    for (i = 0; i < WAVEFORM_LENGTH; i++) {
        sinewave[i] = 511 * (sin(Radians * i) + 1);
    }
    
    REG_PM_APBCMASK |= 0x40000;     /* enable bus clock for DAC */
    REG_GCLK_CLKCTRL = 0x4021;      /* GCLK0 to DAC */
    REG_DAC_CTRLB = 0x41;           /* Vref = AVcc; enable output driver */
    REG_DAC_CTRLA = 2;              /* enable DAC */
    ARRAY_PORT_PINCFG0[2] |= 1;     /* Use PMUX for PA02 */
    ARRAY_PORT_PMUX0[1] = 0x01;     /* PA02 = VOUT */
    
    while (1) {
        for (i = 0; i < WAVEFORM_LENGTH; i++) {
            REG_DAC_DATA = sinewave[i]; /* write value of i to DAC */
        }
    }
}