95 lines
3.1 KiB
C++
95 lines
3.1 KiB
C++
// ---------------------------------------------------------------------------
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// This file is part of reSID, a MOS6581 SID emulator engine.
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// Copyright (C) 2004 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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// ---------------------------------------------------------------------------
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#define __EXTFILT_CC__
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#include "extfilt.h"
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// ----------------------------------------------------------------------------
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// Constructor.
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// ----------------------------------------------------------------------------
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ExternalFilterFP::ExternalFilterFP()
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{
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reset();
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enable_filter(true);
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set_chip_model(MOS6581FP);
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set_clock_frequency(1e6f);
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set_sampling_parameter(15915.6f);
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}
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// ----------------------------------------------------------------------------
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// Enable filter.
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// ----------------------------------------------------------------------------
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void ExternalFilterFP::enable_filter(bool enable)
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{
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enabled = enable;
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}
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// ----------------------------------------------------------------------------
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// Setup of the external filter sampling parameters.
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// ----------------------------------------------------------------------------
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void ExternalFilterFP::set_clock_frequency(float clock)
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{
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clock_frequency = clock;
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_set_sampling_parameter();
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}
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void ExternalFilterFP::set_sampling_parameter(float freq)
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{
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pass_frequency = freq;
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_set_sampling_parameter();
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}
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void ExternalFilterFP::_set_sampling_parameter()
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{
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// Low-pass: R = 10kOhm, C = 1000pF; w0l = 1/RC = 1/(1e4*1e-9) = 100000
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// High-pass: R = 1kOhm, C = 10uF; w0h = 1/RC = 1/(1e3*1e-5) = 100
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w0hp = 100.f / clock_frequency;
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w0lp = pass_frequency * 2.f * M_PI_f / clock_frequency;
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}
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// ----------------------------------------------------------------------------
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// Set chip model.
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// ----------------------------------------------------------------------------
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void ExternalFilterFP::set_chip_model(chip_model model)
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{
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if (model == MOS6581FP) {
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// Approximate the DC output level to be removed if the external
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// filter is turned off. (0x800 - wave_zero + voice DC) * maxenv * voices
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// - extin offset...
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mixer_DC = (-0x600 + 0x800) * 0xff * 3 - 0x20000;
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}
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else {
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// No DC offsets in the MOS8580.
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mixer_DC = 0;
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}
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}
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// ----------------------------------------------------------------------------
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// SID reset.
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// ----------------------------------------------------------------------------
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void ExternalFilterFP::reset()
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{
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// State of filter.
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Vlp = 0;
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Vhp = 0;
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Vo = 0;
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}
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