teensy-audio/synth_dc.cpp

/* Audio Library for Teensy 3.X
 * Copyright (c) 2014, Paul Stoffregen, paul@pjrc.com
 *
 * Development of this audio library was funded by PJRC.COM, LLC by sales of
 * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
 * open source software by purchasing Teensy or other PJRC products.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice, development funding notice, and this permission
 * notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "synth_dc.h"

void AudioSynthWaveformDc::update(void)
{
	audio_block_t *block;
	uint32_t *p, *end, val;
	int32_t count, t1, t2, t3, t4;

	block = allocate();
	if (!block) return;
	p = (uint32_t *)(block->data);
	end = p + AUDIO_BLOCK_SAMPLES/2;

	if (state == 0) {
		// steady DC output, simply fill the buffer with fixed value
		val = pack_16t_16t(magnitude, magnitude);
		do {
			*p++ = val;
			*p++ = val;
			*p++ = val;
			*p++ = val;
			*p++ = val;
			*p++ = val;
			*p++ = val;
			*p++ = val;
		} while (p < end);
	} else {
		// transitioning to a new DC level
		//count = (target - magnitude) / increment;
		count = substract_int32_then_divide_int32(target, magnitude, increment);
		if (count >= 128) {
			// this update will not reach the target
			do {
				magnitude += increment;
				t1 = magnitude;
				magnitude += increment;
				t1 = pack_16t_16t(magnitude, t1);
				magnitude += increment;
				t2 = magnitude;
				magnitude += increment;
				t2 = pack_16t_16t(magnitude, t2);
				magnitude += increment;
				t3 = magnitude;
				magnitude += increment;
				t3 = pack_16t_16t(magnitude, t3);
				magnitude += increment;
				t4 = magnitude;
				magnitude += increment;
				t4 = pack_16t_16t(magnitude, t4);
				*p++ = t1;
				*p++ = t2;
				*p++ = t3;
				*p++ = t4;
			} while (p < end);
		} else {
			// this update reaches the target
			while (count >= 2) {
				count -= 2;
				magnitude += increment;
				t1 = magnitude;
				magnitude += increment;
				t1 = pack_16t_16t(magnitude, t1);
				*p++ = t1;
			}
			if (count) {
				t1 = pack_16t_16t(target, magnitude + increment);
				*p++ = t1;
			}
			magnitude = target;
			state = 0;
			val = pack_16t_16t(magnitude, magnitude);
			while (p < end) {
				*p++ = val;
			}
		}
	}
	transmit(block);
	release(block);
}