view projects/d-box/FeedbackOscillator.cpp @ 45:579c86316008 newapi

Major API overhaul. Moved to a single data structure for handling render functions. Functionally, generally similar except for scheduling within PRU loop function, which now uses interrupts from the PRU rather than polling. This requires an updated kernel.

/*
 * FeedbackOscillator.cpp
 *
 * Recursive phase-shift oscillator implemented
 * on the matrix
 *
 * Andrew McPherson 2014
 */

#include "FeedbackOscillator.h"
#include <cstdlib>
#include <cmath>

#define COEFF_B0 	0
#define COEFF_B1	1
#define COEFF_A1	2

FeedbackOscillator::FeedbackOscillator()
: wavetable1(0), wavetable2(0)
{

}

FeedbackOscillator::~FeedbackOscillator() {
	if(wavetable1 != 0)
		free(wavetable1);
	if(wavetable2 != 0)
		free(wavetable2);

}

// Initialise the settings for the feedback oscillator
void FeedbackOscillator::initialise(int maxTableSize, float hpfCutoffFrequency, float matrixSampleRate) {
	wavetableMaxLength = maxTableSize;
	if(wavetable1 != 0)
		free(wavetable1);
	if(wavetable2 != 0)
		free(wavetable2);

	wavetable1 = (float *)malloc(maxTableSize * sizeof(float));
	wavetable2 = (float *)malloc(maxTableSize * sizeof(float));

	float omega = tan(M_PI * hpfCutoffFrequency / matrixSampleRate);
	float n = 1.0f / (1.0f + omega);

	coeffs[COEFF_A1] = (omega - 1.0f) * n;
	coeffs[COEFF_B0] = n;
	coeffs[COEFF_B1] = -n;

	for(int n = 0; n < maxTableSize; n++)
		wavetable1[n] = wavetable2[n] = 0;

	wavetableRead = wavetable1;
	wavetableWrite = wavetable2;
	wavetableWritePointer = 0;
	sampleCount = lastTriggerCount = 0;
}

// Process one sample and store the output value
// Returns true if the wavetable needs rendering
int FeedbackOscillator::process(uint16_t input, uint16_t *output) {
	float inFloat = input / 65536.0;
	float outFloat = coeffs[COEFF_B0] * inFloat + coeffs[COEFF_B1] * lastInput - coeffs[COEFF_A1] * lastOutput;
	int requestRenderLength = 0;

	//outFloat *= 2.0;

	int intOut = outFloat * 65536.0 + 32768;
	if(intOut > 65535)
		intOut = 65535;
	if(intOut < 0)
		intOut = 0;
	//intOut = (intOut & 0xFF) << 8;
	//if(intOut > 65535)
	//	intOut = 65535;

	*output = (uint16_t)intOut;

	if(canTrigger && outFloat > 0 && lastOutput <= 0) {
		triggered = true;
		requestRenderLength = wavetableWritePointer;	// How many samples stored thus far?
		if(requestRenderLength < 4)
			requestRenderLength = 0;	// Ignore anything with fewer than 4 points

		lastTriggerCount = sampleCount;
		canTrigger = false;
		wavetableWritePointer = 0;

		// Swap buffers
		float *temp = wavetableWrite;
		wavetableWrite = wavetableRead;
		wavetableRead = temp;
	}

	if(triggered) {
		wavetableWrite[wavetableWritePointer] = outFloat;
		if(++wavetableWritePointer >= wavetableMaxLength) {
			triggered = false;
			wavetableWritePointer = 0;
		}
	}

	if(sampleCount - lastTriggerCount > 40)
		canTrigger = true;

	sampleCount++;

	lastOutput = outFloat;
	lastInput = inFloat;

	return requestRenderLength;
}