109 lines
3.2 KiB
C++
Executable File
109 lines
3.2 KiB
C++
Executable File
/*
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AudioOutputI2SNoDAC
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Audio player using SW delta-sigma to generate "analog" on I2S data
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Copyright (C) 2017 Earle F. Philhower, III
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <Arduino.h>
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#ifdef ESP32
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#include "driver/i2s.h"
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#else
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#include <i2s.h>
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#endif
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#include "AudioOutputI2SNoDAC.h"
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AudioOutputI2SNoDAC::AudioOutputI2SNoDAC(int port) : AudioOutputI2S(port, false)
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{
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SetOversampling(32);
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lastSamp = 0;
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cumErr = 0;
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#ifndef ESP32
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WRITE_PERI_REG(PERIPHS_IO_MUX_MTDO_U, orig_bck);
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WRITE_PERI_REG(PERIPHS_IO_MUX_GPIO2_U, orig_ws);
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#endif
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}
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AudioOutputI2SNoDAC::~AudioOutputI2SNoDAC()
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{
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}
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bool AudioOutputI2SNoDAC::SetOversampling(int os) {
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if (os % 32) return false; // Only Nx32 oversampling supported
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if (os > 256) return false; // Don't be silly now!
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if (os < 32) return false; // Nothing under 32 allowed
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oversample = os;
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return SetRate(hertz);
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}
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void AudioOutputI2SNoDAC::DeltaSigma(int16_t sample[2], uint32_t dsBuff[8])
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{
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// Not shift 8 because addition takes care of one mult x 2
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int32_t sum = (((int32_t)sample[0]) + ((int32_t)sample[1])) >> 1;
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fixed24p8_t newSamp = ( (int32_t)Amplify(sum) ) << 8;
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int oversample32 = oversample / 32;
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// How much the comparison signal changes each oversample step
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fixed24p8_t diffPerStep = (newSamp - lastSamp) >> (4 + oversample32);
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// Don't need lastSamp anymore, store this one for next round
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lastSamp = newSamp;
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for (int j = 0; j < oversample32; j++) {
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uint32_t bits = 0; // The bits we convert the sample into, MSB to go on the wire first
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for (int i = 32; i > 0; i--) {
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bits = bits << 1;
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if (cumErr < 0) {
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bits |= 1;
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cumErr += fixedPosValue - newSamp;
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} else {
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// Bits[0] = 0 handled already by left shift
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cumErr -= fixedPosValue + newSamp;
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}
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newSamp += diffPerStep; // Move the reference signal towards destination
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}
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dsBuff[j] = bits;
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}
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}
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bool AudioOutputI2SNoDAC::ConsumeSample(int16_t sample[2])
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{
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int16_t ms[2];
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ms[0] = sample[0];
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ms[1] = sample[1];
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MakeSampleStereo16( ms );
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// Make delta-sigma filled buffer
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uint32_t dsBuff[8];
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DeltaSigma(ms, dsBuff);
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// Either send complete pulse stream or nothing
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#ifdef ESP32
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if (!i2s_write_bytes((i2s_port_t)portNo, (const char *)dsBuff, sizeof(uint32_t) * (oversample/32), 0))
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return false;
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#else
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if (!i2s_write_sample_nb(dsBuff[0])) return false; // No room at the inn
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// At this point we've sent in first of possibly 8 32-bits, need to send
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// remaining ones even if they block.
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for (int i = 32; i < oversample; i+=32)
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i2s_write_sample( dsBuff[i / 32]);
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#endif
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return true;
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}
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