143 lines
3.5 KiB
C++
143 lines
3.5 KiB
C++
/*
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* This file is part of libsidplayfp, a SID player engine.
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*
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* Copyright 2011-2022 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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#ifndef INTEGRATOR8580_H
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#define INTEGRATOR8580_H
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#include "FilterModelConfig8580.h"
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#include <stdint.h>
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#include <cassert>
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#include "siddefs-fp.h"
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namespace reSIDfp
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{
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/**
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* 8580 integrator
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*
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* +---C---+
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* | |
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* vi -----Rfc---o--[A>--o-- vo
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* vx
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*
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* IRfc + ICr = 0
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* IRfc + C*(vc - vc0)/dt = 0
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* dt/C*(IRfc) + vc - vc0 = 0
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* vc = vc0 - n*(IRfc(vi,vx))
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* vc = vc0 - n*(IRfc(vi,g(vc)))
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*
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* IRfc = K*W/L*(Vgst^2 - Vgdt^2) = n*((Vddt - vx)^2 - (Vddt - vi)^2)
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*
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* Rfc gate voltage is generated by an OP Amp and depends on chip temperature.
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*/
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class Integrator8580
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{
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private:
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mutable int vx;
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mutable int vc;
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unsigned short nVgt;
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unsigned short n_dac;
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const FilterModelConfig8580* fmc;
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public:
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Integrator8580(const FilterModelConfig8580* fmc) :
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vx(0),
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vc(0),
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fmc(fmc)
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{
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setV(1.5);
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}
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/**
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* Set Filter Cutoff resistor ratio.
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*/
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void setFc(double wl)
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{
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// Normalized current factor, 1 cycle at 1MHz.
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// Fit in 5 bits.
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n_dac = fmc->getNormalizedCurrentFactor(wl);
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}
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/**
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* Set FC gate voltage multiplier.
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*/
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void setV(double v)
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{
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// Gate voltage is controlled by the switched capacitor voltage divider
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// Ua = Ue * v = 4.76v 1<v<2
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assert(v > 1.0 && v < 2.0);
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const double Vg = fmc->getVoiceDCVoltage() * v;
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const double Vgt = Vg - fmc->getVth();
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// Vg - Vth, normalized so that translated values can be subtracted:
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// Vgt - x = (Vgt - t) - (x - t)
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nVgt = fmc->getNormalizedValue(Vgt);
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}
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int solve(int vi) const;
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};
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} // namespace reSIDfp
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#if RESID_INLINING || defined(INTEGRATOR8580_CPP)
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namespace reSIDfp
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{
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RESID_INLINE
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int Integrator8580::solve(int vi) const
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{
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// Make sure we're not in subthreshold mode
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assert(vx < nVgt);
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// DAC voltages
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const unsigned int Vgst = nVgt - vx;
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const unsigned int Vgdt = (vi < nVgt) ? nVgt - vi : 0; // triode/saturation mode
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const unsigned int Vgst_2 = Vgst * Vgst;
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const unsigned int Vgdt_2 = Vgdt * Vgdt;
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// DAC current, scaled by (1/m)*2^13*m*2^16*m*2^16*2^-15 = m*2^30
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const int n_I_dac = n_dac * (static_cast<int>(Vgst_2 - Vgdt_2) >> 15);
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// Change in capacitor charge.
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vc += n_I_dac;
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// vx = g(vc)
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const int tmp = (vc >> 15) + (1 << 15);
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assert(tmp < (1 << 16));
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vx = fmc->getOpampRev(tmp);
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// Return vo.
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return vx - (vc >> 14);
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}
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} // namespace reSIDfp
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#endif
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#endif
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