335 lines
8.5 KiB
C++
335 lines
8.5 KiB
C++
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
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#include "Sap_Apu.h"
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#include <string.h>
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/* Copyright (C) 2006 Shay Green. This module is free software; you
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can redistribute it and/or modify it under the terms of the GNU Lesser
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General Public License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version. This
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module is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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details. You should have received a copy of the GNU Lesser General Public
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License along with this module; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
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#include "blargg_source.h"
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int const max_frequency = 12000; // pure waves above this frequency are silenced
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static void gen_poly( blargg_ulong mask, int count, byte* out )
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{
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blargg_ulong n = 1;
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do
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{
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int bits = 0;
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int b = 0;
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do
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{
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// implemented using "Galios configuration"
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bits |= (n & 1) << b;
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n = (n >> 1) ^ (mask & -(n & 1));
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}
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while ( b++ < 7 );
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*out++ = bits;
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}
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while ( --count );
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}
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// poly5
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int const poly5_len = (1 << 5) - 1;
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blargg_ulong const poly5_mask = (1UL << poly5_len) - 1;
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blargg_ulong const poly5 = 0x167C6EA1;
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inline blargg_ulong run_poly5( blargg_ulong in, int shift )
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{
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return (in << shift & poly5_mask) | (in >> (poly5_len - shift));
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}
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#define POLY_MASK( width, tap1, tap2 ) \
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((1UL << (width - 1 - tap1)) | (1UL << (width - 1 - tap2)))
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Sap_Apu_Impl::Sap_Apu_Impl()
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{
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gen_poly( POLY_MASK( 4, 1, 0 ), sizeof poly4, poly4 );
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gen_poly( POLY_MASK( 9, 5, 0 ), sizeof poly9, poly9 );
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gen_poly( POLY_MASK( 17, 5, 0 ), sizeof poly17, poly17 );
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if ( 0 ) // comment out to recauculate poly5 constant
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{
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byte poly5 [4];
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gen_poly( POLY_MASK( 5, 2, 0 ), sizeof poly5, poly5 );
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blargg_ulong n = poly5 [3] * 0x1000000L + poly5 [2] * 0x10000L +
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poly5 [1] * 0x100L + poly5 [0];
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blargg_ulong rev = n & 1;
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for ( int i = 1; i < poly5_len; i++ )
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rev |= (n >> i & 1) << (poly5_len - i);
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debug_printf( "poly5: 0x%08lX\n", rev );
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}
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}
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Sap_Apu::Sap_Apu()
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{
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impl = 0;
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for ( int i = 0; i < osc_count; i++ )
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osc_output( i, 0 );
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}
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void Sap_Apu::reset( Sap_Apu_Impl* new_impl )
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{
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impl = new_impl;
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last_time = 0;
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poly5_pos = 0;
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poly4_pos = 0;
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polym_pos = 0;
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control = 0;
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for ( int i = 0; i < osc_count; i++ )
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memset( &oscs [i], 0, offsetof (osc_t,output) );
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}
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inline void Sap_Apu::calc_periods()
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{
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// 15/64 kHz clock
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int divider = 28;
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if ( this->control & 1 )
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divider = 114;
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for ( int i = 0; i < osc_count; i++ )
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{
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osc_t* const osc = &oscs [i];
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int const osc_reload = osc->regs [0]; // cache
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blargg_long period = (osc_reload + 1) * divider;
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static byte const fast_bits [osc_count] = { 1 << 6, 1 << 4, 1 << 5, 1 << 3 };
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if ( this->control & fast_bits [i] )
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{
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period = osc_reload + 4;
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if ( i & 1 )
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{
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period = osc_reload * 0x100L + osc [-1].regs [0] + 7;
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if ( !(this->control & fast_bits [i - 1]) )
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period = (period - 6) * divider;
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if ( (osc [-1].regs [1] & 0x1F) > 0x10 )
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debug_printf( "Use of slave channel in 16-bit mode not supported\n" );
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}
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}
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osc->period = period;
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}
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}
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void Sap_Apu::run_until( blip_time_t end_time )
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{
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calc_periods();
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Sap_Apu_Impl* const impl = this->impl; // cache
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// 17/9-bit poly selection
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byte const* polym = impl->poly17;
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int polym_len = poly17_len;
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if ( this->control & 0x80 )
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{
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polym_len = poly9_len;
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polym = impl->poly9;
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}
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polym_pos %= polym_len;
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for ( int i = 0; i < osc_count; i++ )
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{
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osc_t* const osc = &oscs [i];
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blip_time_t time = last_time + osc->delay;
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blip_time_t const period = osc->period;
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// output
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Blip_Buffer* output = osc->output;
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if ( output )
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{
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output->set_modified();
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int const osc_control = osc->regs [1]; // cache
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int volume = (osc_control & 0x0F) * 2;
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if ( !volume || osc_control & 0x10 || // silent, DAC mode, or inaudible frequency
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((osc_control & 0xA0) == 0xA0 && period < 1789773 / 2 / max_frequency) )
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{
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if ( !(osc_control & 0x10) )
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volume >>= 1; // inaudible frequency = half volume
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int delta = volume - osc->last_amp;
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if ( delta )
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{
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osc->last_amp = volume;
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impl->synth.offset( last_time, delta, output );
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}
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// TODO: doesn't maintain high pass flip-flop (very minor issue)
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}
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else
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{
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// high pass
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static byte const hipass_bits [osc_count] = { 1 << 2, 1 << 1, 0, 0 };
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blip_time_t period2 = 0; // unused if no high pass
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blip_time_t time2 = end_time;
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if ( this->control & hipass_bits [i] )
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{
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period2 = osc [2].period;
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time2 = last_time + osc [2].delay;
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if ( osc->invert )
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{
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// trick inner wave loop into inverting output
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osc->last_amp -= volume;
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volume = -volume;
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}
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}
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if ( time < end_time || time2 < end_time )
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{
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// poly source
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static byte const poly1 [] = { 0x55, 0x55 }; // square wave
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byte const* poly = poly1;
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int poly_len = 8 * sizeof poly1; // can be just 2 bits, but this is faster
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int poly_pos = osc->phase & 1;
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int poly_inc = 1;
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if ( !(osc_control & 0x20) )
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{
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poly = polym;
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poly_len = polym_len;
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poly_pos = polym_pos;
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if ( osc_control & 0x40 )
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{
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poly = impl->poly4;
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poly_len = poly4_len;
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poly_pos = poly4_pos;
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}
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poly_inc = period % poly_len;
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poly_pos = (poly_pos + osc->delay) % poly_len;
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}
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poly_inc -= poly_len; // allows more optimized inner loop below
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// square/poly5 wave
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blargg_ulong wave = poly5;
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check( poly5 & 1 ); // low bit is set for pure wave
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int poly5_inc = 0;
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if ( !(osc_control & 0x80) )
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{
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wave = run_poly5( wave, (osc->delay + poly5_pos) % poly5_len );
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poly5_inc = period % poly5_len;
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}
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// Run wave and high pass interleved with each catching up to the other.
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// Disabled high pass has no performance effect since inner wave loop
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// makes no compromise for high pass, and only runs once in that case.
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int osc_last_amp = osc->last_amp;
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do
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{
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// run high pass
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if ( time2 < time )
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{
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int delta = -osc_last_amp;
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if ( volume < 0 )
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delta += volume;
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if ( delta )
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{
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osc_last_amp += delta - volume;
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volume = -volume;
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impl->synth.offset( time2, delta, output );
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}
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}
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while ( time2 <= time ) // must advance *past* time to avoid hang
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time2 += period2;
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// run wave
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blip_time_t end = end_time;
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if ( end > time2 )
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end = time2;
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while ( time < end )
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{
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if ( wave & 1 )
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{
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int amp = volume & -(poly [poly_pos >> 3] >> (poly_pos & 7) & 1);
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if ( (poly_pos += poly_inc) < 0 )
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poly_pos += poly_len;
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int delta = amp - osc_last_amp;
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if ( delta )
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{
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osc_last_amp = amp;
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impl->synth.offset( time, delta, output );
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}
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}
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wave = run_poly5( wave, poly5_inc );
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time += period;
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}
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}
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while ( time < end_time || time2 < end_time );
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osc->phase = poly_pos;
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osc->last_amp = osc_last_amp;
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}
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osc->invert = 0;
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if ( volume < 0 )
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{
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// undo inversion trickery
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osc->last_amp -= volume;
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osc->invert = 1;
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}
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}
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}
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// maintain divider
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blip_time_t remain = end_time - time;
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if ( remain > 0 )
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{
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blargg_long count = (remain + period - 1) / period;
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osc->phase ^= count;
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time += count * period;
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}
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osc->delay = time - end_time;
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}
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// advance polies
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blip_time_t duration = end_time - last_time;
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last_time = end_time;
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poly4_pos = (poly4_pos + duration) % poly4_len;
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poly5_pos = (poly5_pos + duration) % poly5_len;
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polym_pos += duration; // will get %'d on next call
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}
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void Sap_Apu::write_data( blip_time_t time, unsigned addr, int data )
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{
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run_until( time );
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int i = (addr ^ 0xD200) >> 1;
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if ( i < osc_count )
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{
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oscs [i].regs [addr & 1] = data;
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}
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else if ( addr == 0xD208 )
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{
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control = data;
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}
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else if ( addr == 0xD209 )
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{
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oscs [0].delay = 0;
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oscs [1].delay = 0;
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oscs [2].delay = 0;
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oscs [3].delay = 0;
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}
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/*
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// TODO: are polynomials reset in this case?
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else if ( addr == 0xD20F )
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{
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if ( (data & 3) == 0 )
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polym_pos = 0;
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}
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*/
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}
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void Sap_Apu::end_frame( blip_time_t end_time )
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{
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if ( end_time > last_time )
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run_until( end_time );
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last_time -= end_time;
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}
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