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[Core/Sound] improved accuracy of SN76489 core

This commit is contained in:
EkeEke 2017-03-28 16:15:45 +02:00
parent e7e231955c
commit b78ce06728
3 changed files with 19 additions and 9 deletions
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24
core/sound/psg.c
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@ -6,7 +6,7 @@
*
* Noise implementation based on http://www.smspower.org/Development/SN76489#NoiseChannel
*
* Copyright (C) 2016 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2016-2017 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
@ -78,6 +78,7 @@ static struct
{
int clocks;
int latch;
int zeroFreqInc;
int noiseShiftValue;
int noiseShiftWidth;
int noiseBitMask;
@ -100,9 +101,12 @@ void psg_init(PSG_TYPE type)
for (i=0; i<4; i++)
{
psg.chanAmp[i][0] = 100;
psg.chanAmp[i][1] = 100;
psg.chanAmp[i][1] = 100;
}
/* Initialize Tone zero frequency increment value */
psg.zeroFreqInc = ((type == PSG_DISCRETE) ? 0x400 : 0x1) * PSG_MCYCLES_RATIO;
/* Initialize Noise LSFR type */
psg.noiseShiftWidth = noiseShiftWidth[type];
psg.noiseBitMask = noiseBitMask[type];
@ -117,7 +121,7 @@ void psg_reset()
{
psg.regs[i*2] = 0;
psg.regs[i*2+1] = 0;
psg.freqInc[i] = (i < 3) ? (1 * PSG_MCYCLES_RATIO) : (16 * PSG_MCYCLES_RATIO);
psg.freqInc[i] = (i < 3) ? (psg.zeroFreqInc) : (16 * PSG_MCYCLES_RATIO);
psg.freqCounter[i] = 0;
psg.polarity[i] = -1;
psg.chanDelta[i][0] = 0;
@ -298,8 +302,8 @@ void psg_write(unsigned int clocks, unsigned int data)
}
else
{
/* zero value behaves the same as a value of 1 (verified on integrated version only) */
psg.freqInc[index>>1] = PSG_MCYCLES_RATIO;
/* zero value behaves the same as a value of 1 on integrated version (0x400 on discrete version) */
psg.freqInc[index>>1] = psg.zeroFreqInc;
}
/* update noise channel counter increment if required */
@ -328,7 +332,15 @@ void psg_write(unsigned int clocks, unsigned int data)
psg.freqInc[3] = (0x10 << noiseFreq) * PSG_MCYCLES_RATIO;
}
/* reset shift register value */
/* check current noise shift register output */
if (psg.noiseShiftValue & 1)
{
/* high to low transition will be applied at next internal cycle update */
psg.chanDelta[3][0] = -psg.chanOut[3][0];
psg.chanDelta[3][1] = -psg.chanOut[3][1];
}
/* reset noise shift register value (noise channel output is forced low) */
psg.noiseShiftValue = 1 << psg.noiseShiftWidth;;
break;

2
core/sound/psg.h
View File

@ -6,7 +6,7 @@
*
* Noise implementation based on http://www.smspower.org/Development/SN76489#NoiseChannel
*
* Copyright (C) 2016 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2016-2017 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:

2
sdl/README.txt
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@ -116,8 +116,6 @@ END USERS SHOULD PREFERABLY USE LIBRETRO PORT WITH RETROARCH.
Original YM2612/YM2413 cores by Jarek Burczynski & Tatsuyuki Satoh
Original SN76489 core by Maxim
Original SVP core by Notaz
Blip Buffer & NTSC Video filter libraries by Shay Green (Blargg)