mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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127 lines
4.1 KiB
C
127 lines
4.1 KiB
C
/***************************************************************************************
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* Genesis Plus
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*
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* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald (original code)
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* Eke-Eke (2007,2008,2009), additional code & fixes for the GCN/Wii port
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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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* Sound Hardware
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****************************************************************************************/
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#include "shared.h"
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#include "Fir_Resampler.h"
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/* cycle-accurate samples */
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static int m68cycles_per_sample[2];
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/* return the number of samples that should be retrieved */
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static inline int fm_sample_cnt(uint8 z80)
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{
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if (z80) return ((((count_z80 + current_z80 - z80_ICount) * 15) / (m68cycles_per_sample[0] * 7)) - snd.fm.pos);
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else return ((count_m68k / m68cycles_per_sample[0]) - snd.fm.pos);
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}
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static inline int psg_sample_cnt(uint8 z80)
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{
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if (z80) return ((((count_z80 + current_z80 - z80_ICount) * 15) / (m68cycles_per_sample[1] * 7)) - snd.psg.pos);
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else return ((count_m68k / m68cycles_per_sample[1]) - snd.psg.pos);
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}
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/* run FM chip for n samples */
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static inline void fm_update(int cnt)
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{
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if (cnt > 0)
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{
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YM2612Update(cnt);
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snd.fm.pos += cnt;
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}
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}
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/* run PSG chip for n samples */
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static inline void psg_update(int cnt)
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{
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if (cnt > 0)
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{
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SN76489_Update(snd.psg.buffer + snd.psg.pos, cnt);
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snd.psg.pos += cnt;
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}
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}
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/* initialize sound chips emulation */
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void sound_init(int rate)
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{
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double vclk = (vdp_pal ? (double)CLOCK_PAL : (double)CLOCK_NTSC) / 7.0; /* 68000 and YM2612 clock */
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double zclk = (vdp_pal ? (double)CLOCK_PAL : (double)CLOCK_NTSC) / 15.0; /* Z80 and SN76489 clock */
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/* cycle-accurate FM & PSG samples */
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m68cycles_per_sample[0] = (int)(((double)m68cycles_per_line * (double)lines_per_frame * (double)vdp_rate / (double)rate) + 0.5);
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m68cycles_per_sample[1] = m68cycles_per_sample[0];
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/* YM2612 is emulated at its original frequency (VLCK/144) */
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if (config.hq_fm)
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{
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m68cycles_per_sample[0] = 144;
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/* "real" ratio is (vclk/144.0)/(rate) but this causes scratchy sound in Wii/GCN 50Hz video mode */
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/* since "real" framerate is lower than 50 fps whereas PAL Wii/GCN framerate is higher than 50 fps */
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/* it's better to directly use the ratio between generated & expected numbers of samples per frame */
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Fir_Resampler_time_ratio((double)m68cycles_per_line * (double)lines_per_frame * (double)vdp_rate / 144.0 / (double)rate);
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}
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/* initialize sound chips */
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SN76489_Init((int)zclk,rate);
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YM2612Init((int)vclk,rate);
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}
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void sound_update(int fm_len, int psg_len)
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{
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/* update last samples (if needed) */
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fm_update(fm_len - snd.fm.pos);
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psg_update(psg_len - snd.psg.pos);
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/* reset samples count */
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snd.fm.pos = 0;
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snd.psg.pos = 0;
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}
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/* reset FM chip */
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void fm_reset(void)
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{
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fm_update(fm_sample_cnt(0));
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YM2612ResetChip();
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}
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/* write FM chip */
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void fm_write(unsigned int cpu, unsigned int address, unsigned int data)
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{
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if (address & 1) fm_update(fm_sample_cnt(cpu));
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YM2612Write(address, data);
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}
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/* read FM status */
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unsigned int fm_read(unsigned int cpu, unsigned int address)
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{
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fm_update(fm_sample_cnt(cpu));
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return YM2612Read();
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}
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/* write PSG chip */
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void psg_write(unsigned int cpu, unsigned int data)
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{
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psg_update(psg_sample_cnt(cpu));
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SN76489_Write(data);
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}
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