137 lines
4.2 KiB
C++
137 lines
4.2 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 2011-2023 Leandro Nini <drfiemost@users.sourceforge.net>
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* Copyright 2007-2010 Antti Lankila
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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 WAVEFORMCALCULATOR_h
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#define WAVEFORMCALCULATOR_h
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#include <map>
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#include "array.h"
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#include "sidcxx11.h"
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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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* Combined waveform model parameters.
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*/
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typedef struct
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{
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float threshold;
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float pulsestrength;
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float distance1;
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float distance2;
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} CombinedWaveformConfig;
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/**
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* Combined waveform calculator for WaveformGenerator.
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* By combining waveforms, the bits of each waveform are effectively short
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* circuited. A zero bit in one waveform will result in a zero output bit
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* (thus the infamous claim that the waveforms are AND'ed).
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* However, a zero bit in one waveform may also affect the neighboring bits
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* in the output.
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*
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* Example:
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*
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* 1 1
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* Bit # 1 0 9 8 7 6 5 4 3 2 1 0
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* -----------------------
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* Sawtooth 0 0 0 1 1 1 1 1 1 0 0 0
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*
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* Triangle 0 0 1 1 1 1 1 1 0 0 0 0
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*
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* AND 0 0 0 1 1 1 1 1 0 0 0 0
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*
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* Output 0 0 0 0 1 1 1 0 0 0 0 0
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*
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*
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* Re-vectorized die photographs reveal the mechanism behind this behavior.
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* Each waveform selector bit acts as a switch, which directly connects
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* internal outputs into the waveform DAC inputs as follows:
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*
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* - Noise outputs the shift register bits to DAC inputs as described above.
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* Each output is also used as input to the next bit when the shift register
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* is shifted. Lower four bits are grounded.
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* - Pulse connects a single line to all DAC inputs. The line is connected to
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* either 5V (pulse on) or 0V (pulse off) at bit 11, and ends at bit 0.
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* - Triangle connects the upper 11 bits of the (MSB EOR'ed) accumulator to the
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* DAC inputs, so that DAC bit 0 = 0, DAC bit n = accumulator bit n - 1.
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* - Sawtooth connects the upper 12 bits of the accumulator to the DAC inputs,
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* so that DAC bit n = accumulator bit n. Sawtooth blocks out the MSB from
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* the EOR used to generate the triangle waveform.
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*
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* We can thus draw the following conclusions:
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*
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* - The shift register may be written to by combined waveforms.
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* - The pulse waveform interconnects all bits in combined waveforms via the
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* pulse line.
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* - The combination of triangle and sawtooth interconnects neighboring bits
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* of the sawtooth waveform.
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*
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* Also in the 6581 the MSB of the oscillator, used as input for the
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* triangle xor logic and the pulse adder's last bit, is connected directly
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* to the waveform selector, while in the 8580 it is latched at sid_clk2
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* before being forwarded to the selector. Thus in the 6581 if the sawtooth MSB
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* is pulled down it might affect the oscillator's adder
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* driving the top bit low.
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*
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*/
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class WaveformCalculator
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{
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private:
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typedef std::map<const CombinedWaveformConfig*, matrix_t> cw_cache_t;
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private:
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matrix_t wftable;
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cw_cache_t PULLDOWN_CACHE;
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private:
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WaveformCalculator();
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public:
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/**
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* Get the singleton instance.
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*/
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static WaveformCalculator* getInstance();
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/**
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* Get the waveform table for use by WaveformGenerator.
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*
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* @return Waveform table
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*/
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matrix_t* getWaveTable() { return &wftable; }
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/**
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* Build pulldown table for use by WaveformGenerator.
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*
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* @param model Chip model to use
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* @return Pulldown table
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*/
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matrix_t* buildPulldownTable(ChipModel model);
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};
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} // namespace reSIDfp
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#endif
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