102 lines
3.0 KiB
C++
102 lines
3.0 KiB
C++
#include <Arduino.h>
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#include "DDS.h"
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// To start the DDS, we use Timer1, set to the reference clock
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// We use Timer2 for the PWM output, running as fast as feasible
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void DDS::start() {
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// Use the clkIO clock rate
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ASSR &= ~(_BV(EXCLK) | _BV(AS2));
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// First, the timer for the PWM output
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// Setup the timer to use OC2B (pin 3) in fast PWM mode with a configurable top
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// Run it without the prescaler
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TCCR2A = (TCCR2A | _BV(COM2B1)) & ~(_BV(COM2B0) | _BV(COM2A1) | _BV(COM2A0)) |
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_BV(WGM21) | _BV(WGM20);
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TCCR2B = (TCCR2B & ~(_BV(CS22) | _BV(CS21))) | _BV(CS20) | _BV(WGM22);
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// Set the top limit, which will be our duty cycle accuracy.
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// Setting Comparator Bits smaller will allow for higher frequency PWM,
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// with the loss of resolution.
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OCR2A = pow(2,COMPARATOR_BITS)-1;
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OCR2B = 0;
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// Second, setup Timer1 to trigger the ADC interrupt
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// This lets us use decoding functions that run at the same reference
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// clock as the DDS.
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TCCR1B = _BV(CS11) | _BV(WGM13) | _BV(WGM12);
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TCCR1A = 0;
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ICR1 = ((F_CPU / 8) / DDS_REFCLK_DEAULT) - 1;
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// Configure the ADC here to automatically run and be triggered off Timer1
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ADMUX = _BV(REFS0) | _BV(ADLAR) | 0; // Channel 0, shift result left (ADCH used)
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DDRC &= ~_BV(0);
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PORTC &= ~_BV(0);
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DIDR0 |= _BV(0);
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ADCSRB = _BV(ADTS2) | _BV(ADTS1) | _BV(ADTS0);
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ADCSRA = _BV(ADEN) | _BV(ADSC) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2); // | _BV(ADPS0);
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}
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void DDS::stop() {
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// TODO: Stop the timers.
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}
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// Set our current sine wave frequency in Hz
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void DDS::setFrequency(unsigned short freq) {
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// Fo = (M*Fc)/2^N
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// M = (Fo/Fc)*2^N
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if(refclk == DDS_REFCLK_DEAULT) {
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// Try to use precalculated values if possible
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if(freq == 2200) {
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stepRate = (2200.0 / DDS_REFCLK_DEAULT) * pow(2,ACCUMULATOR_BITS);
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} else if (freq == 1200) {
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stepRate = (1200.0 / DDS_REFCLK_DEAULT) * pow(2,ACCUMULATOR_BITS);
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}
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} else {
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// Do the actual math instead.
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stepRate = (freq / refclk) * pow(2,ACCUMULATOR_BITS);
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}
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}
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// TODO: Clean this up a bit..
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void DDS::clockTick() {
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if(running) {
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accumulator += stepRate;
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if(timeLimited && tickDuration == 0) {
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#ifdef DDS_IDLE_HIGH
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// Set the duty cycle to 50%
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OCR2B = pow(2,COMPARATOR_BITS)/2;
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#else
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// Set duty cycle to 0, effectively off
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OCR2B = 0;
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#endif
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running = false;
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accumulator = 0;
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} else {
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OCR2B = getDutyCycle();
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}
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// Reduce our playback duration by one tick
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tickDuration--;
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} else {
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// Hold it low
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#ifdef DDS_IDLE_HIGH
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// Set the duty cycle to 50%
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OCR2B = pow(2,COMPARATOR_BITS)/2;
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#else
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// Set duty cycle to 0, effectively off
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OCR2B = 0;
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#endif
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}
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}
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uint8_t DDS::getDutyCycle() {
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#if ACCUMULATOR_BIT_SHIFT >= 24
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uint16_t phAng;
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#else
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uint8_t phAng;
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#endif
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phAng = (accumulator >> ACCUMULATOR_BIT_SHIFT);
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uint8_t position = pgm_read_byte_near(ddsSineTable + phAng)>>(8-COMPARATOR_BITS);
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// Apply scaling and return
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return position >> amplitude;
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}
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