mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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292 lines
10 KiB
C
292 lines
10 KiB
C
/*
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SN76489 emulation
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by Maxim in 2001 and 2002
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converted from my original Delphi implementation
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I'm a C newbie so I'm sure there are loads of stupid things
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in here which I'll come back to some day and redo
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Includes:
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- Super-high quality tone channel "oversampling" by calculating fractional positions on transitions
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- Noise output pattern reverse engineered from actual SMS output
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- Volume levels taken from actual SMS output
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07/08/04 Charles MacDonald
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Modified for use with SMS Plus:
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- Added support for multiple PSG chips.
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- Added reset/config/update routines.
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- Added context management routines.
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- Removed SN76489_GetValues().
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- Removed some unused variables.
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25/04/07 Eke-Eke
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Modified for use with GenesisPlus Gamecube's port:
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- made SN76489_Update outputs 16bits mono samples
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- replaced volume table with VGM plugin's one
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*/
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#include "shared.h"
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#include <float.h> // for FLT_MIN
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#include <string.h> // for memcpy
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#define NoiseInitialState 0x8000 /* Initial state of shift register */
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#define PSG_CUTOFF 0x6 /* Value below which PSG does not output */
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static const int PSGVolumeValues[2][16] = {
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/* These values are taken from a real SMS2's output */
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{892,892,892,760,623,497,404,323,257,198,159,123,96,75,60,0}, /* I can't remember why 892... :P some scaling I did at some point */
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/* these values are true volumes for 2dB drops at each step (multiply previous by 10^-0.1), normalised at 760 */
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{1516,1205,957,760,603,479,381,303,240,191,152,120,96,76,60,0}
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};
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static SN76489_Context SN76489[MAX_SN76489];
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void SN76489_Init(int which, int PSGClockValue, int SamplingRate)
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{
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SN76489_Context *p = &SN76489[which];
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p->dClock=(float)PSGClockValue/16/SamplingRate;
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SN76489_Config(which, MUTE_ALLON, VOL_FULL, FB_SEGAVDP, SRW_SEGAVDP, 1);
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SN76489_Reset(which);
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}
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void SN76489_Reset(int which)
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{
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SN76489_Context *p = &SN76489[which];
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int i;
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p->PSGStereo = 0xFF;
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for(i = 0; i <= 3; i++)
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{
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/* Initialise PSG state */
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p->Registers[2*i] = 1; /* tone freq=1 */
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p->Registers[2*i+1] = 0xf; /* vol=off */
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p->NoiseFreq = 0x10;
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/* Set counters to 0 */
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p->ToneFreqVals[i] = 0;
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/* Set flip-flops to 1 */
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p->ToneFreqPos[i] = 1;
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/* Set intermediate positions to do-not-use value */
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p->IntermediatePos[i] = FLT_MIN;
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/* Set panning to centre */
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p->panning[0]=127;
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}
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p->LatchedRegister=0;
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/* Initialise noise generator */
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p->NoiseShiftRegister=NoiseInitialState;
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/* Zero clock */
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p->Clock=0;
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}
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void SN76489_Shutdown(void)
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{
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}
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void SN76489_Config(int which, int mute, int volume, int feedback, int sr_width, int boost_noise)
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{
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SN76489_Context *p = &SN76489[which];
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p->Mute = mute;
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p->VolumeArray = volume;
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p->WhiteNoiseFeedback = feedback;
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p->SRWidth = sr_width;
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p->BoostNoise = boost_noise;
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}
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void SN76489_SetContext(int which, uint8 *data)
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{
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memcpy(&SN76489[which], data, sizeof(SN76489_Context));
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}
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void SN76489_GetContext(int which, uint8 *data)
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{
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memcpy(data, &SN76489[which], sizeof(SN76489_Context));
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}
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uint8 *SN76489_GetContextPtr(int which)
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{
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return (uint8 *)&SN76489[which];
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}
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int SN76489_GetContextSize(void)
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{
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return sizeof(SN76489_Context);
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}
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void SN76489_Write(int which, int data)
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{
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SN76489_Context *p = &SN76489[which];
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if (data&0x80) {
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/* Latch/data byte %1 cc t dddd */
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p->LatchedRegister=((data>>4)&0x07);
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p->Registers[p->LatchedRegister]=
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(p->Registers[p->LatchedRegister] & 0x3f0) /* zero low 4 bits */
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| (data&0xf); /* and replace with data */
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} else {
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/* Data byte %0 - dddddd */
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if (!(p->LatchedRegister%2)&&(p->LatchedRegister<5))
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/* Tone register */
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p->Registers[p->LatchedRegister]=
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(p->Registers[p->LatchedRegister] & 0x00f) /* zero high 6 bits */
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| ((data&0x3f)<<4); /* and replace with data */
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else
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/* Other register */
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p->Registers[p->LatchedRegister]=data&0x0f; /* Replace with data */
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}
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switch (p->LatchedRegister) {
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case 0:
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case 2:
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case 4: /* Tone channels */
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if (p->Registers[p->LatchedRegister]==0) p->Registers[p->LatchedRegister]=1; /* Zero frequency changed to 1 to avoid div/0 */
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break;
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case 6: /* Noise */
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p->NoiseShiftRegister=NoiseInitialState; /* reset shift register */
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p->NoiseFreq=0x10<<(p->Registers[6]&0x3); /* set noise signal generator frequency */
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break;
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}
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}
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void SN76489_GGStereoWrite(int which, int data)
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{
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SN76489_Context *p = &SN76489[which];
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p->PSGStereo=data;
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}
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void SN76489_Update(int which, INT16 *buffer, int length)
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{
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SN76489_Context *p = &SN76489[which];
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int i, j;
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for(j = 0; j < length; j++)
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{
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for (i=0;i<=2;++i)
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if (p->IntermediatePos[i]!=FLT_MIN)
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p->Channels[i]=(short)((p->Mute >> i & 0x1)*PSGVolumeValues[p->VolumeArray][p->Registers[2*i+1]]*p->IntermediatePos[i]);
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else
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p->Channels[i]=(p->Mute >> i & 0x1)*PSGVolumeValues[p->VolumeArray][p->Registers[2*i+1]]*p->ToneFreqPos[i];
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p->Channels[3]=(short)((p->Mute >> 3 & 0x1)*PSGVolumeValues[p->VolumeArray][p->Registers[7]]*(p->NoiseShiftRegister & 0x1));
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if (p->BoostNoise) p->Channels[3]<<=1; /* double noise volume */
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buffer[j] =0;
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for (i=0;i<=3;++i) buffer[j] += p->Channels[i];
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p->Clock+=p->dClock;
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p->NumClocksForSample=(int)p->Clock; /* truncates */
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p->Clock-=p->NumClocksForSample; /* remove integer part */
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/* Looks nicer in Delphi... */
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/* Clock:=Clock+p->dClock; */
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/* NumClocksForSample:=Trunc(Clock); */
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/* Clock:=Frac(Clock); */
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/* Decrement tone channel counters */
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for (i=0;i<=2;++i)
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p->ToneFreqVals[i]-=p->NumClocksForSample;
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/* Noise channel: match to tone2 or decrement its counter */
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if (p->NoiseFreq==0x80) p->ToneFreqVals[3]=p->ToneFreqVals[2];
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else p->ToneFreqVals[3]-=p->NumClocksForSample;
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/* Tone channels: */
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for (i=0;i<=2;++i) {
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if (p->ToneFreqVals[i]<=0) { /* If it gets below 0... */
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if (p->Registers[i*2]>PSG_CUTOFF) {
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/* Calculate how much of the sample is + and how much is - */
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/* Go to floating point and include the clock fraction for extreme accuracy :D */
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/* Store as long int, maybe it's faster? I'm not very good at this */
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p->IntermediatePos[i]=(p->NumClocksForSample-p->Clock+2*p->ToneFreqVals[i])*p->ToneFreqPos[i]/(p->NumClocksForSample+p->Clock);
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p->ToneFreqPos[i]=-p->ToneFreqPos[i]; /* Flip the flip-flop */
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} else {
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p->ToneFreqPos[i]=1; /* stuck value */
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p->IntermediatePos[i]=FLT_MIN;
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}
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p->ToneFreqVals[i]+=p->Registers[i*2]*(p->NumClocksForSample/p->Registers[i*2]+1);
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} else p->IntermediatePos[i]=FLT_MIN;
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}
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/* Noise channel */
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if (p->ToneFreqVals[3]<=0) { /* If it gets below 0... */
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p->ToneFreqPos[3]=-p->ToneFreqPos[3]; /* Flip the flip-flop */
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if (p->NoiseFreq!=0x80) /* If not matching tone2, decrement counter */
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p->ToneFreqVals[3]+=p->NoiseFreq*(p->NumClocksForSample/p->NoiseFreq+1);
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if (p->ToneFreqPos[3]==1) { /* Only once per cycle... */
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int Feedback;
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if (p->Registers[6]&0x4) { /* White noise */
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/* Calculate parity of fed-back bits for feedback */
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switch (p->WhiteNoiseFeedback) {
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/* Do some optimised calculations for common (known) feedback values */
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case 0x0003: /* SC-3000, BBC %00000011 */
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case 0x0009: /* SMS, GG, MD %00001001 */
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/* If two bits fed back, I can do Feedback=(nsr & fb) && (nsr & fb ^ fb) */
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/* since that's (one or more bits set) && (not all bits set) */
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Feedback=((p->NoiseShiftRegister&p->WhiteNoiseFeedback) && ((p->NoiseShiftRegister&p->WhiteNoiseFeedback)^p->WhiteNoiseFeedback));
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break;
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default: /* Default handler for all other feedback values */
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Feedback=p->NoiseShiftRegister&p->WhiteNoiseFeedback;
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Feedback^=Feedback>>8;
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Feedback^=Feedback>>4;
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Feedback^=Feedback>>2;
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Feedback^=Feedback>>1;
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Feedback&=1;
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break;
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}
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} else /* Periodic noise */
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Feedback=p->NoiseShiftRegister&1;
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p->NoiseShiftRegister=(p->NoiseShiftRegister>>1) | (Feedback << (p->SRWidth-1));
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/* Original code: */
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/* p->NoiseShiftRegister=(p->NoiseShiftRegister>>1) | ((p->Registers[6]&0x4?((p->NoiseShiftRegister&0x9) && (p->NoiseShiftRegister&0x9^0x9)):p->NoiseShiftRegister&1)<<15); */
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}
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}
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}
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}
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/*void SN76489_UpdateOne(int which, int *l, int *r)
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{
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INT16 tl,tr;
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INT16 *buff[2]={&tl,&tr};
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SN76489_Update(which,buff,1);
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*l=tl;
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*r=tr;
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}*/
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int SN76489_GetMute(int which)
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{
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return SN76489[which].Mute;
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}
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void SN76489_SetMute(int which, int val)
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{
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SN76489[which].Mute=val;
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}
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int SN76489_GetVolType(int which)
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{
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return SN76489[which].VolumeArray;
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}
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void SN76489_SetVolType(int which, int val)
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{
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SN76489[which].VolumeArray=val;
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}
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void SN76489_SetPanning(int which, int ch0, int ch1, int ch2, int ch3)
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{
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SN76489[which].panning[0]=ch0;
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SN76489[which].panning[1]=ch1;
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SN76489[which].panning[2]=ch2;
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SN76489[which].panning[3]=ch3;
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}
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