123 lines
3.2 KiB
Text
123 lines
3.2 KiB
Text
/*
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* This file is part of libsidplayfp, a SID player engine.
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*
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* Copyright 2011-2016 Leandro Nini <drfiemost@users.sourceforge.net>
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* Copyright 2007-2010 Antti Lankila
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* Copyright 2004,2010 Dag Lem <resid@nimrod.no>
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*
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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 2 of the License, or
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* (at your option) any later version.
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*
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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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*
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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, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include "Dac.h"
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namespace reSIDfp
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{
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Dac::Dac(unsigned int bits) :
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dac(new double[bits]),
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dacLength(bits)
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{}
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Dac::~Dac()
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{
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delete [] dac;
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}
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double Dac::getOutput(unsigned int input) const
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{
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double dacValue = 0.;
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for (unsigned int i = 0; i < dacLength; i++)
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{
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if ((input & (1 << i)) != 0)
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{
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dacValue += dac[i];
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}
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}
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return dacValue;
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}
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void Dac::kinkedDac(ChipModel chipModel)
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{
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const double R_INFINITY = 1e6;
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// Non-linearity parameter, 8580 DACs are perfectly linear
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const double _2R_div_R = chipModel == MOS6581 ? 2.20 : 2.00;
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// 6581 DACs are not terminated by a 2R resistor
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const bool term = chipModel == MOS8580;
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// Calculate voltage contribution by each individual bit in the R-2R ladder.
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for (unsigned int set_bit = 0; set_bit < dacLength; set_bit++)
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{
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double Vn = 1.; // Normalized bit voltage.
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double R = 1.; // Normalized R
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const double _2R = _2R_div_R * R; // 2R
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double Rn = term ? // Rn = 2R for correct termination,
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_2R : R_INFINITY; // INFINITY for missing termination.
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unsigned int bit;
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// Calculate DAC "tail" resistance by repeated parallel substitution.
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for (bit = 0; bit < set_bit; bit++)
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{
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Rn = (Rn == R_INFINITY) ?
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R + _2R :
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R + _2R * Rn / (_2R + Rn); // R + 2R || Rn
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}
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// Source transformation for bit voltage.
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if (Rn == R_INFINITY)
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{
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Rn = _2R;
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}
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else
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{
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Rn = _2R * Rn / (_2R + Rn); // 2R || Rn
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Vn = Vn * Rn / _2R;
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}
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// Calculate DAC output voltage by repeated source transformation from
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// the "tail".
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for (++bit; bit < dacLength; bit++)
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{
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Rn += R;
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const double I = Vn / Rn;
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Rn = _2R * Rn / (_2R + Rn); // 2R || Rn
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Vn = Rn * I;
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}
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dac[set_bit] = Vn;
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}
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// Normalize to integerish behavior
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double Vsum = 0.;
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for (unsigned int i = 0; i < dacLength; i++)
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{
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Vsum += dac[i];
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}
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Vsum /= 1 << dacLength;
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for (unsigned int i = 0; i < dacLength; i++)
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{
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dac[i] /= Vsum;
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}
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}
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} // namespace reSIDfp
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