forked from len0rd/rockbox
13cbade08a
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30397 a1c6a512-1295-4272-9138-f99709370657
138 lines
3.8 KiB
C
138 lines
3.8 KiB
C
// Nes_Snd_Emu 0.1.8. http://www.slack.net/~ant/
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#include "nes_namco_apu.h"
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/* Copyright (C) 2003-2006 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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void Namco_init( struct Nes_Namco_Apu* this )
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{
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Synth_init( &this->synth );
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Namco_output( this, NULL );
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Namco_volume( this, (int)FP_ONE_VOLUME );
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Namco_reset( this );
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}
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void Namco_reset( struct Nes_Namco_Apu* this )
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{
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this->last_time = 0;
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this->addr_reg = 0;
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int i;
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for ( i = 0; i < namco_reg_count; i++ )
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this->reg [i] = 0;
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for ( i = 0; i < namco_osc_count; i++ )
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{
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struct Namco_Osc* osc = &this->oscs [i];
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osc->delay = 0;
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osc->last_amp = 0;
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osc->wave_pos = 0;
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}
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}
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void Namco_output( struct Nes_Namco_Apu* this, struct Blip_Buffer* buf )
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{
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int i;
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for ( i = 0; i < namco_osc_count; i++ )
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Namco_osc_output( this, i, buf );
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}
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void Namco_end_frame( struct Nes_Namco_Apu* this, blip_time_t time )
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{
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if ( time > this->last_time )
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Namco_run_until( this, time );
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assert( this->last_time >= time );
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this->last_time -= time;
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}
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void Namco_run_until( struct Nes_Namco_Apu* this, blip_time_t nes_end_time )
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{
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int active_oscs = (this->reg [0x7F] >> 4 & 7) + 1;
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int i;
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for ( i = namco_osc_count - active_oscs; i < namco_osc_count; i++ )
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{
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struct Namco_Osc* osc = &this->oscs [i];
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struct Blip_Buffer* output = osc->output;
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if ( !output )
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continue;
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blip_resampled_time_t time =
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Blip_resampled_time( output, this->last_time ) + osc->delay;
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blip_resampled_time_t end_time = Blip_resampled_time( output, nes_end_time );
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osc->delay = 0;
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if ( time < end_time )
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{
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const uint8_t* osc_reg = &this->reg [i * 8 + 0x40];
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if ( !(osc_reg [4] & 0xE0) )
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continue;
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int volume = osc_reg [7] & 15;
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if ( !volume )
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continue;
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int freq = (osc_reg [4] & 3) * 0x10000 + osc_reg [2] * 0x100L + osc_reg [0];
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if ( freq < 64 * active_oscs )
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continue; // prevent low frequencies from excessively delaying freq changes
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int const master_clock_divider = 12; // NES time derived via divider of master clock
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int const n106_divider = 45; // N106 then divides master clock by this
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int const max_freq = 0x3FFFF;
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int const lowest_freq_period = (max_freq + 1) * n106_divider / master_clock_divider;
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// divide by 8 to avoid overflow
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blip_resampled_time_t period =
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Blip_resampled_duration( output, lowest_freq_period / 8 ) / freq * 8 * active_oscs;
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int wave_size = 32 - (osc_reg [4] >> 2 & 7) * 4;
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if ( !wave_size )
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continue;
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int last_amp = osc->last_amp;
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int wave_pos = osc->wave_pos;
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Blip_set_modified( output );
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do
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{
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// read wave sample
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int addr = wave_pos + osc_reg [6];
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int sample = this->reg [addr >> 1] >> (addr << 2 & 4);
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wave_pos++;
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sample = (sample & 15) * volume;
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// output impulse if amplitude changed
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int delta = sample - last_amp;
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if ( delta )
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{
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last_amp = sample;
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Synth_offset_resampled( &this->synth, time, delta, output );
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}
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// next sample
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time += period;
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if ( wave_pos >= wave_size )
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wave_pos = 0;
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}
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while ( time < end_time );
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osc->wave_pos = wave_pos;
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osc->last_amp = last_amp;
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}
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osc->delay = time - end_time;
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}
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this->last_time = nes_end_time;
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}
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