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395 lines
11 KiB
C++
395 lines
11 KiB
C++
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
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#include "Ay_Apu.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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// Emulation inaccuracies:
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// * Noise isn't run when not in use
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// * Changes to envelope and noise periods are delayed until next reload
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// * Super-sonic tone should attenuate output to about 60%, not 50%
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// Tones above this frequency are treated as disabled tone at half volume.
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// Power of two is more efficient (avoids division).
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unsigned const inaudible_freq = 16384;
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int const period_factor = 16;
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static byte const amp_table [16] =
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{
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#define ENTRY( n ) byte (n * Ay_Apu::amp_range + 0.5)
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// With channels tied together and 1K resistor to ground (as datasheet recommends),
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// output nearly matches logarithmic curve as claimed. Approx. 1.5 dB per step.
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ENTRY(0.000000),ENTRY(0.007813),ENTRY(0.011049),ENTRY(0.015625),
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ENTRY(0.022097),ENTRY(0.031250),ENTRY(0.044194),ENTRY(0.062500),
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ENTRY(0.088388),ENTRY(0.125000),ENTRY(0.176777),ENTRY(0.250000),
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ENTRY(0.353553),ENTRY(0.500000),ENTRY(0.707107),ENTRY(1.000000),
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/*
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// Measured from an AY-3-8910A chip with date code 8611.
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// Direct voltages without any load (very linear)
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ENTRY(0.000000),ENTRY(0.046237),ENTRY(0.064516),ENTRY(0.089785),
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ENTRY(0.124731),ENTRY(0.173118),ENTRY(0.225806),ENTRY(0.329032),
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ENTRY(0.360215),ENTRY(0.494624),ENTRY(0.594624),ENTRY(0.672043),
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ENTRY(0.766129),ENTRY(0.841935),ENTRY(0.926882),ENTRY(1.000000),
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// With only some load
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ENTRY(0.000000),ENTRY(0.011940),ENTRY(0.017413),ENTRY(0.024876),
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ENTRY(0.036318),ENTRY(0.054229),ENTRY(0.072637),ENTRY(0.122388),
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ENTRY(0.174129),ENTRY(0.239303),ENTRY(0.323881),ENTRY(0.410945),
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ENTRY(0.527363),ENTRY(0.651741),ENTRY(0.832338),ENTRY(1.000000),
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*/
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#undef ENTRY
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};
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static byte const modes [8] =
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{
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#define MODE( a0,a1, b0,b1, c0,c1 ) \
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(a0 | a1<<1 | b0<<2 | b1<<3 | c0<<4 | c1<<5)
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MODE( 1,0, 1,0, 1,0 ),
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MODE( 1,0, 0,0, 0,0 ),
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MODE( 1,0, 0,1, 1,0 ),
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MODE( 1,0, 1,1, 1,1 ),
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MODE( 0,1, 0,1, 0,1 ),
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MODE( 0,1, 1,1, 1,1 ),
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MODE( 0,1, 1,0, 0,1 ),
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MODE( 0,1, 0,0, 0,0 ),
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};
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Ay_Apu::Ay_Apu()
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{
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// build full table of the upper 8 envelope waveforms
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for ( int m = 8; m--; )
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{
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byte* out = env.modes [m];
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int flags = modes [m];
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for ( int x = 3; --x >= 0; )
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{
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int amp = flags & 1;
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int end = flags >> 1 & 1;
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int step = end - amp;
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amp *= 15;
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for ( int y = 16; --y >= 0; )
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{
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*out++ = amp_table [amp];
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amp += step;
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}
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flags >>= 2;
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}
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}
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output( 0 );
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volume( 1.0 );
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reset();
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}
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void Ay_Apu::reset()
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{
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last_time = 0;
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noise.delay = 0;
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noise.lfsr = 1;
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osc_t* osc = &oscs [osc_count];
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do
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{
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osc--;
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osc->period = period_factor;
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osc->delay = 0;
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osc->last_amp = 0;
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osc->phase = 0;
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}
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while ( osc != oscs );
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for ( int i = sizeof regs; --i >= 0; )
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regs [i] = 0;
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regs [7] = 0xFF;
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write_data_( 13, 0 );
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}
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void Ay_Apu::write_data_( int addr, int data )
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{
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assert( (unsigned) addr < reg_count );
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if ( (unsigned) addr >= 14 )
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{
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#ifdef debug_printf
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debug_printf( "Wrote to I/O port %02X\n", (int) addr );
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#endif
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}
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// envelope mode
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if ( addr == 13 )
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{
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if ( !(data & 8) ) // convert modes 0-7 to proper equivalents
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data = (data & 4) ? 15 : 9;
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env.wave = env.modes [data - 7];
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env.pos = -48;
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env.delay = 0; // will get set to envelope period in run_until()
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}
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regs [addr] = data;
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// handle period changes accurately
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int i = addr >> 1;
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if ( i < osc_count )
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{
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blip_time_t period = (regs [i * 2 + 1] & 0x0F) * (0x100L * period_factor) +
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regs [i * 2] * period_factor;
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if ( !period )
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period = period_factor;
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// adjust time of next timer expiration based on change in period
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osc_t& osc = oscs [i];
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if ( (osc.delay += period - osc.period) < 0 )
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osc.delay = 0;
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osc.period = period;
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}
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// TODO: same as above for envelope timer, and it also has a divide by two after it
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}
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int const noise_off = 0x08;
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int const tone_off = 0x01;
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void Ay_Apu::run_until( blip_time_t final_end_time )
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{
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require( final_end_time >= last_time );
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// noise period and initial values
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blip_time_t const noise_period_factor = period_factor * 2; // verified
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blip_time_t noise_period = (regs [6] & 0x1F) * noise_period_factor;
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if ( !noise_period )
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noise_period = noise_period_factor;
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blip_time_t const old_noise_delay = noise.delay;
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blargg_ulong const old_noise_lfsr = noise.lfsr;
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// envelope period
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blip_time_t const env_period_factor = period_factor * 2; // verified
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blip_time_t env_period = (regs [12] * 0x100L + regs [11]) * env_period_factor;
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if ( !env_period )
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env_period = env_period_factor; // same as period 1 on my AY chip
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if ( !env.delay )
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env.delay = env_period;
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// run each osc separately
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for ( int index = 0; index < osc_count; index++ )
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{
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osc_t* const osc = &oscs [index];
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int osc_mode = regs [7] >> index;
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// output
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Blip_Buffer* const osc_output = osc->output;
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if ( !osc_output )
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continue;
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osc_output->set_modified();
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// period
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int half_vol = 0;
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blip_time_t inaudible_period = (blargg_ulong) (osc_output->clock_rate() +
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inaudible_freq) / (inaudible_freq * 2);
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if ( osc->period <= inaudible_period && !(osc_mode & tone_off) )
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{
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half_vol = 1; // Actually around 60%, but 50% is close enough
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osc_mode |= tone_off;
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}
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// envelope
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blip_time_t start_time = last_time;
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blip_time_t end_time = final_end_time;
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int const vol_mode = regs [0x08 + index];
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int volume = amp_table [vol_mode & 0x0F] >> half_vol;
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int osc_env_pos = env.pos;
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if ( vol_mode & 0x10 )
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{
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volume = env.wave [osc_env_pos] >> half_vol;
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// use envelope only if it's a repeating wave or a ramp that hasn't finished
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if ( !(regs [13] & 1) || osc_env_pos < -32 )
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{
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end_time = start_time + env.delay;
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if ( end_time >= final_end_time )
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end_time = final_end_time;
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//if ( !(regs [12] | regs [11]) )
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// debug_printf( "Used envelope period 0\n" );
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}
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else if ( !volume )
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{
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osc_mode = noise_off | tone_off;
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}
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}
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else if ( !volume )
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{
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osc_mode = noise_off | tone_off;
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}
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// tone time
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blip_time_t const period = osc->period;
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blip_time_t time = start_time + osc->delay;
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if ( osc_mode & tone_off ) // maintain tone's phase when off
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{
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blargg_long count = (final_end_time - time + period - 1) / period;
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time += count * period;
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osc->phase ^= count & 1;
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}
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// noise time
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blip_time_t ntime = final_end_time;
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blargg_ulong noise_lfsr = 1;
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if ( !(osc_mode & noise_off) )
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{
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ntime = start_time + old_noise_delay;
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noise_lfsr = old_noise_lfsr;
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//if ( (regs [6] & 0x1F) == 0 )
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// debug_printf( "Used noise period 0\n" );
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}
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// The following efficiently handles several cases (least demanding first):
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// * Tone, noise, and envelope disabled, where channel acts as 4-bit DAC
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// * Just tone or just noise, envelope disabled
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// * Envelope controlling tone and/or noise
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// * Tone and noise disabled, envelope enabled with high frequency
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// * Tone and noise together
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// * Tone and noise together with envelope
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// This loop only runs one iteration if envelope is disabled. If envelope
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// is being used as a waveform (tone and noise disabled), this loop will
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// still be reasonably efficient since the bulk of it will be skipped.
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while ( 1 )
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{
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// current amplitude
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int amp = 0;
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if ( (osc_mode | osc->phase) & 1 & (osc_mode >> 3 | noise_lfsr) )
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amp = volume;
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{
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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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synth_.offset( start_time, delta, osc_output );
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}
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}
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// Run wave and noise interleved with each catching up to the other.
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// If one or both are disabled, their "current time" will be past end time,
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// so there will be no significant performance hit.
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if ( ntime < end_time || time < end_time )
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{
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// Since amplitude was updated above, delta will always be +/- volume,
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// so we can avoid using last_amp every time to calculate the delta.
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int delta = amp * 2 - volume;
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int delta_non_zero = delta != 0;
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int phase = osc->phase | (osc_mode & tone_off); assert( tone_off == 0x01 );
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do
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{
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// run noise
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blip_time_t end = end_time;
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if ( end_time > time ) end = time;
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if ( phase & delta_non_zero )
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{
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while ( ntime <= end ) // must advance *past* time to avoid hang
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{
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int changed = noise_lfsr + 1;
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noise_lfsr = (-(noise_lfsr & 1) & 0x12000) ^ (noise_lfsr >> 1);
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if ( changed & 2 )
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{
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delta = -delta;
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synth_.offset( ntime, delta, osc_output );
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}
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ntime += noise_period;
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}
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}
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else
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{
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// 20 or more noise periods on average for some music
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blargg_long remain = end - ntime;
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blargg_long count = remain / noise_period;
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if ( remain >= 0 )
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ntime += noise_period + count * noise_period;
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}
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// run tone
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end = end_time;
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if ( end_time > ntime ) end = ntime;
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if ( noise_lfsr & delta_non_zero )
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{
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while ( time < end )
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{
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delta = -delta;
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synth_.offset( time, delta, osc_output );
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time += period;
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//phase ^= 1;
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}
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//assert( phase == (delta > 0) );
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phase = unsigned (-delta) >> (CHAR_BIT * sizeof (unsigned) - 1);
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// (delta > 0)
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}
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else
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{
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// loop usually runs less than once
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//SUB_CASE_COUNTER( (time < end) * (end - time + period - 1) / period );
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while ( time < end )
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{
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time += period;
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phase ^= 1;
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}
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}
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}
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while ( time < end_time || ntime < end_time );
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osc->last_amp = (delta + volume) >> 1;
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if ( !(osc_mode & tone_off) )
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osc->phase = phase;
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}
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if ( end_time >= final_end_time )
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break; // breaks first time when envelope is disabled
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// next envelope step
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if ( ++osc_env_pos >= 0 )
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osc_env_pos -= 32;
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volume = env.wave [osc_env_pos] >> half_vol;
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start_time = end_time;
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end_time += env_period;
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if ( end_time > final_end_time )
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end_time = final_end_time;
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}
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osc->delay = time - final_end_time;
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if ( !(osc_mode & noise_off) )
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{
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noise.delay = ntime - final_end_time;
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noise.lfsr = noise_lfsr;
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}
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}
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// TODO: optimized saw wave envelope?
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// maintain envelope phase
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blip_time_t remain = final_end_time - last_time - env.delay;
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if ( remain >= 0 )
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{
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blargg_long count = (remain + env_period) / env_period;
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env.pos += count;
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if ( env.pos >= 0 )
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env.pos = (env.pos & 31) - 32;
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remain -= count * env_period;
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assert( -remain <= env_period );
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}
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env.delay = -remain;
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assert( env.delay > 0 );
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assert( env.pos < 0 );
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last_time = final_end_time;
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}
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