mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-09 12:25:16 +01:00
452 lines
12 KiB
C
452 lines
12 KiB
C
/*
|
|
SN76489 emulation
|
|
by Maxim in 2001 and 2002
|
|
converted from my original Delphi implementation
|
|
|
|
I'm a C newbie so I'm sure there are loads of stupid things
|
|
in here which I'll come back to some day and redo
|
|
|
|
Includes:
|
|
- Super-high quality tone channel "oversampling" by calculating fractional positions on transitions
|
|
- Noise output pattern reverse engineered from actual SMS output
|
|
- Volume levels taken from actual SMS output
|
|
|
|
07/08/04 Charles MacDonald
|
|
Modified for use with SMS Plus:
|
|
- Added support for multiple PSG chips.
|
|
- Added reset/config/update routines.
|
|
- Added context management routines.
|
|
- Removed SN76489_GetValues().
|
|
- Removed some unused variables.
|
|
|
|
25/04/07 Eke-Eke (Genesis Plus GX)
|
|
- Removed stereo GG support (unused)
|
|
- Made SN76489_Update outputs 16bits mono samples
|
|
- Replaced volume table with VGM plugin's one
|
|
|
|
05/01/09 Eke-Eke (Genesis Plus GX)
|
|
- Modified Cut-Off frequency (according to Steve Snake: http://www.smspower.org/forums/viewtopic.php?t=1746)
|
|
|
|
24/08/10 Eke-Eke (Genesis Plus GX)
|
|
- Removed multichip support (unused)
|
|
- Removed alternate volume table, panning & mute support (unused)
|
|
- Removed configurable Feedback and Shift Register Width (always use Sega ones)
|
|
- Added linear resampling using Blip Buffer (based on Blargg's implementation: http://www.smspower.org/forums/viewtopic.php?t=11376)
|
|
|
|
01/09/12 Eke-Eke (Genesis Plus GX)
|
|
- Added generic Blip-Buffer support internally, using common Master Clock as timebase
|
|
- Re-added stereo GG support
|
|
- Re-added configurable Feedback and Shift Register Width
|
|
- Rewrote core with various optimizations
|
|
*/
|
|
|
|
#include "shared.h"
|
|
|
|
#define PSG_MCYCLES_RATIO (16 * 15)
|
|
|
|
/* Initial state of shift register */
|
|
#define NoiseInitialState 0x8000
|
|
|
|
/* Value below which PSG does not output */
|
|
/*#define PSG_CUTOFF 0x6*/
|
|
#define PSG_CUTOFF 0x1
|
|
|
|
/* original Texas Instruments TMS SN76489AN (rev. A) used in SG-1000, SC-3000H & SF-7000 computers */
|
|
#define FB_DISCRETE 0x0006
|
|
#define SRW_DISCRETE 15
|
|
|
|
/* SN76489AN clone integrated in Sega's VDP chips (315-5124, 315-5246, 315-5313, Game Gear) */
|
|
#define FB_SEGAVDP 0x0009
|
|
#define SRW_SEGAVDP 16
|
|
|
|
typedef struct
|
|
{
|
|
/* Configuration */
|
|
int PreAmp[4][2]; /* stereo channels pre-amplification ratio (%) */
|
|
int NoiseFeedback;
|
|
int SRWidth;
|
|
|
|
/* PSG registers: */
|
|
int Registers[8]; /* Tone, vol x4 */
|
|
int LatchedRegister;
|
|
int NoiseShiftRegister;
|
|
int NoiseFreq; /* Noise channel signal generator frequency */
|
|
|
|
/* Output calculation variables */
|
|
int ToneFreqVals[4]; /* Frequency register values (counters) */
|
|
int ToneFreqPos[4]; /* Frequency channel flip-flops */
|
|
int Channel[4][2]; /* current amplitude of each (stereo) channel */
|
|
int ChanOut[4][2]; /* current output value of each (stereo) channel */
|
|
|
|
/* Internal M-clock counter */
|
|
unsigned long clocks;
|
|
|
|
} SN76489_Context;
|
|
|
|
static const uint16 PSGVolumeValues[16] =
|
|
{
|
|
/* These values are taken from a real SMS2's output */
|
|
/*{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 */
|
|
/* these values are true volumes for 2dB drops at each step (multiply previous by 10^-0.1) */
|
|
1516,1205,957,760,603,479,381,303,240,191,152,120,96,76,60,0
|
|
};
|
|
|
|
static SN76489_Context SN76489;
|
|
|
|
static blip_t* blip[2];
|
|
|
|
void SN76489_Init(blip_t* left, blip_t* right, int type)
|
|
{
|
|
int i;
|
|
|
|
blip[0] = left;
|
|
blip[1] = right;
|
|
|
|
for (i=0; i<4; i++)
|
|
{
|
|
SN76489.PreAmp[i][0] = 100;
|
|
SN76489.PreAmp[i][1] = 100;
|
|
}
|
|
|
|
if (type == SN_DISCRETE)
|
|
{
|
|
SN76489.NoiseFeedback = FB_DISCRETE;
|
|
SN76489.SRWidth = SRW_DISCRETE;
|
|
}
|
|
else
|
|
{
|
|
SN76489.NoiseFeedback = FB_SEGAVDP;
|
|
SN76489.SRWidth = SRW_SEGAVDP;
|
|
}
|
|
}
|
|
|
|
void SN76489_Reset()
|
|
{
|
|
int i;
|
|
|
|
for(i = 0; i <= 3; i++)
|
|
{
|
|
/* Initialise PSG state */
|
|
SN76489.Registers[2*i] = 1; /* tone freq=1 */
|
|
SN76489.Registers[2*i+1] = 0xf; /* vol=off */
|
|
|
|
/* Set counters to 0 */
|
|
SN76489.ToneFreqVals[i] = 0;
|
|
|
|
/* Set flip-flops to 1 */
|
|
SN76489.ToneFreqPos[i] = 1;
|
|
|
|
/* Clear stereo channels amplitude */
|
|
SN76489.Channel[i][0] = 0;
|
|
SN76489.Channel[i][1] = 0;
|
|
|
|
/* Clear stereo channel outputs in delta buffer */
|
|
SN76489.ChanOut[i][0] = 0;
|
|
SN76489.ChanOut[i][1] = 0;
|
|
}
|
|
|
|
/* Initialise latched register index */
|
|
SN76489.LatchedRegister = 0;
|
|
|
|
/* Initialise noise generator */
|
|
SN76489.NoiseShiftRegister=NoiseInitialState;
|
|
SN76489.NoiseFreq = 0x10;
|
|
|
|
/* Reset internal M-cycle counter */
|
|
SN76489.clocks = 0;
|
|
}
|
|
|
|
void *SN76489_GetContextPtr(void)
|
|
{
|
|
return (uint8 *)&SN76489;
|
|
}
|
|
|
|
int SN76489_GetContextSize(void)
|
|
{
|
|
return sizeof(SN76489_Context);
|
|
}
|
|
|
|
/* Updates tone amplitude in delta buffer. Call whenever amplitude might have changed. */
|
|
INLINE void UpdateToneAmplitude(int i, int time)
|
|
{
|
|
int delta;
|
|
|
|
/* left output */
|
|
delta = (SN76489.Channel[i][0] * SN76489.ToneFreqPos[i]) - SN76489.ChanOut[i][0];
|
|
if (delta != 0)
|
|
{
|
|
SN76489.ChanOut[i][0] += delta;
|
|
blip_add_delta_fast(blip[0], time, delta);
|
|
}
|
|
|
|
/* right output */
|
|
delta = (SN76489.Channel[i][1] * SN76489.ToneFreqPos[i]) - SN76489.ChanOut[i][1];
|
|
if (delta != 0)
|
|
{
|
|
SN76489.ChanOut[i][1] += delta;
|
|
blip_add_delta_fast(blip[1], time, delta);
|
|
}
|
|
}
|
|
|
|
/* Updates noise amplitude in delta buffer. Call whenever amplitude might have changed. */
|
|
INLINE void UpdateNoiseAmplitude(int time)
|
|
{
|
|
int delta;
|
|
|
|
/* left output */
|
|
delta = (SN76489.Channel[3][0] * ( SN76489.NoiseShiftRegister & 0x1 )) - SN76489.ChanOut[3][0];
|
|
if (delta != 0)
|
|
{
|
|
SN76489.ChanOut[3][0] += delta;
|
|
blip_add_delta_fast(blip[0], time, delta);
|
|
}
|
|
|
|
/* right output */
|
|
delta = (SN76489.Channel[3][1] * ( SN76489.NoiseShiftRegister & 0x1 )) - SN76489.ChanOut[3][1];
|
|
if (delta != 0)
|
|
{
|
|
SN76489.ChanOut[3][1] += delta;
|
|
blip_add_delta_fast(blip[1], time, delta);
|
|
}
|
|
}
|
|
|
|
/* Runs tone channel for clock_length clocks */
|
|
static void RunTone(int i, int clocks)
|
|
{
|
|
int time;
|
|
|
|
/* Update in case a register changed etc. */
|
|
UpdateToneAmplitude(i, SN76489.clocks);
|
|
|
|
/* Time of next transition */
|
|
time = SN76489.ToneFreqVals[i];
|
|
|
|
/* Process any transitions that occur within clocks we're running */
|
|
while (time < clocks)
|
|
{
|
|
if (SN76489.Registers[i*2]>PSG_CUTOFF) {
|
|
/* Flip the flip-flop */
|
|
SN76489.ToneFreqPos[i] = -SN76489.ToneFreqPos[i];
|
|
} else {
|
|
/* stuck value */
|
|
SN76489.ToneFreqPos[i] = 1;
|
|
}
|
|
UpdateToneAmplitude(i, time);
|
|
|
|
/* Advance to time of next transition */
|
|
time += SN76489.Registers[i*2] * PSG_MCYCLES_RATIO;
|
|
}
|
|
|
|
/* Update channel tone counter */
|
|
SN76489.ToneFreqVals[i] = time;
|
|
}
|
|
|
|
/* Runs noise channel for clock_length clocks */
|
|
static void RunNoise(int clocks)
|
|
{
|
|
int time;
|
|
|
|
/* Noise channel: match to tone2 if in slave mode */
|
|
int NoiseFreq = SN76489.NoiseFreq;
|
|
if (NoiseFreq == 0x80)
|
|
{
|
|
NoiseFreq = SN76489.Registers[2*2];
|
|
SN76489.ToneFreqVals[3] = SN76489.ToneFreqVals[2];
|
|
}
|
|
|
|
/* Update in case a register changed etc. */
|
|
UpdateNoiseAmplitude(SN76489.clocks);
|
|
|
|
/* Time of next transition */
|
|
time = SN76489.ToneFreqVals[3];
|
|
|
|
/* Process any transitions that occur within clocks we're running */
|
|
while (time < clocks)
|
|
{
|
|
/* Flip the flip-flop */
|
|
SN76489.ToneFreqPos[3] = -SN76489.ToneFreqPos[3];
|
|
if (SN76489.ToneFreqPos[3] == 1)
|
|
{
|
|
/* On the positive edge of the square wave (only once per cycle) */
|
|
int Feedback = SN76489.NoiseShiftRegister;
|
|
if ( SN76489.Registers[6] & 0x4 )
|
|
{
|
|
/* White noise */
|
|
/* Calculate parity of fed-back bits for feedback */
|
|
/* Do some optimised calculations for common (known) feedback values */
|
|
/* If two bits fed back, I can do Feedback=(nsr & fb) && (nsr & fb ^ fb) */
|
|
/* since that's (one or more bits set) && (not all bits set) */
|
|
Feedback = ((Feedback & SN76489.NoiseFeedback) && ((Feedback & SN76489.NoiseFeedback) ^ SN76489.NoiseFeedback));
|
|
}
|
|
else /* Periodic noise */
|
|
Feedback = Feedback & 1;
|
|
|
|
SN76489.NoiseShiftRegister = (SN76489.NoiseShiftRegister >> 1) | (Feedback << (SN76489.SRWidth - 1));
|
|
UpdateNoiseAmplitude(time);
|
|
}
|
|
|
|
/* Advance to time of next transition */
|
|
time += NoiseFreq * PSG_MCYCLES_RATIO;
|
|
}
|
|
|
|
/* Update channel tone counter */
|
|
SN76489.ToneFreqVals[3] = time;
|
|
}
|
|
|
|
static void SN76489_RunUntil(unsigned int clocks)
|
|
{
|
|
int i;
|
|
|
|
/* Run noise first, since it might use current value of third tone frequency counter */
|
|
RunNoise(clocks);
|
|
|
|
/* Run tone channels */
|
|
for (i=0; i<3; ++i)
|
|
{
|
|
RunTone(i, clocks);
|
|
}
|
|
}
|
|
|
|
void SN76489_Config(unsigned int clocks, int preAmp, int boostNoise, int stereo)
|
|
{
|
|
int i;
|
|
|
|
/* cycle-accurate Game Gear stereo */
|
|
if (clocks > SN76489.clocks)
|
|
{
|
|
/* Run chip until current timestamp */
|
|
SN76489_RunUntil(clocks);
|
|
|
|
/* Update internal M-cycle counter */
|
|
SN76489.clocks += ((clocks - SN76489.clocks + PSG_MCYCLES_RATIO - 1) / PSG_MCYCLES_RATIO) * PSG_MCYCLES_RATIO;
|
|
}
|
|
|
|
for (i=0; i<4; i++)
|
|
{
|
|
/* stereo channel pre-amplification */
|
|
SN76489.PreAmp[i][0] = preAmp * ((stereo >> (i + 4)) & 1);
|
|
SN76489.PreAmp[i][1] = preAmp * ((stereo >> (i + 0)) & 1);
|
|
|
|
/* noise channel boost */
|
|
if (i == 3)
|
|
{
|
|
SN76489.PreAmp[3][0] = SN76489.PreAmp[3][0] << boostNoise;
|
|
SN76489.PreAmp[3][1] = SN76489.PreAmp[3][1] << boostNoise;
|
|
}
|
|
|
|
/* update stereo channel amplitude */
|
|
SN76489.Channel[i][0]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][0]) / 100;
|
|
SN76489.Channel[i][1]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][1]) / 100;
|
|
}
|
|
}
|
|
|
|
void SN76489_Update(unsigned int clocks)
|
|
{
|
|
int i;
|
|
|
|
if (clocks > SN76489.clocks)
|
|
{
|
|
/* Run chip until current timestamp */
|
|
SN76489_RunUntil(clocks);
|
|
|
|
/* Update internal M-cycle counter */
|
|
SN76489.clocks += ((clocks - SN76489.clocks + PSG_MCYCLES_RATIO - 1) / PSG_MCYCLES_RATIO) * PSG_MCYCLES_RATIO;
|
|
}
|
|
|
|
/* Adjust internal M-cycle counter for next frame */
|
|
SN76489.clocks -= clocks;
|
|
|
|
/* Adjust channel time counters for new frame */
|
|
for (i=0; i<4; ++i)
|
|
{
|
|
SN76489.ToneFreqVals[i] -= clocks;
|
|
}
|
|
}
|
|
|
|
void SN76489_Write(unsigned int clocks, unsigned int data)
|
|
{
|
|
unsigned int index;
|
|
|
|
if (clocks > SN76489.clocks)
|
|
{
|
|
/* run chip until current timestamp */
|
|
SN76489_RunUntil(clocks);
|
|
|
|
/* update internal M-cycle counter */
|
|
SN76489.clocks += ((clocks - SN76489.clocks + PSG_MCYCLES_RATIO - 1) / PSG_MCYCLES_RATIO) * PSG_MCYCLES_RATIO;
|
|
}
|
|
|
|
if (data & 0x80)
|
|
{
|
|
/* latch byte %1 cc t dddd */
|
|
SN76489.LatchedRegister = index = (data >> 4) & 0x07;
|
|
}
|
|
else
|
|
{
|
|
/* restore latched register index */
|
|
index = SN76489.LatchedRegister;
|
|
}
|
|
|
|
switch (index)
|
|
{
|
|
case 0:
|
|
case 2:
|
|
case 4: /* Tone Channels frequency */
|
|
{
|
|
if (data & 0x80)
|
|
{
|
|
/* Data byte %1 cc t dddd */
|
|
SN76489.Registers[index] = (SN76489.Registers[index] & 0x3f0) | (data & 0xf);
|
|
}
|
|
else
|
|
{
|
|
/* Data byte %0 - dddddd */
|
|
SN76489.Registers[index] = (SN76489.Registers[index] & 0x00f) | ((data & 0x3f) << 4);
|
|
}
|
|
|
|
/* zero frequency behaves the same as a value of 1 */
|
|
if (SN76489.Registers[index] == 0)
|
|
{
|
|
SN76489.Registers[index] = 1;
|
|
}
|
|
break;
|
|
}
|
|
|
|
case 1:
|
|
case 3:
|
|
case 5: /* Tone Channels attenuation */
|
|
{
|
|
data &= 0x0f;
|
|
SN76489.Registers[index] = data;
|
|
data = PSGVolumeValues[data];
|
|
index >>= 1;
|
|
SN76489.Channel[index][0] = (data * SN76489.PreAmp[index][0]) / 100;
|
|
SN76489.Channel[index][1] = (data * SN76489.PreAmp[index][1]) / 100;
|
|
break;
|
|
}
|
|
|
|
case 6: /* Noise control */
|
|
{
|
|
SN76489.Registers[6] = data & 0x0f;
|
|
|
|
/* reset shift register */
|
|
SN76489.NoiseShiftRegister = NoiseInitialState;
|
|
|
|
/* set noise signal generator frequency */
|
|
SN76489.NoiseFreq = 0x10 << (data&0x3);
|
|
break;
|
|
}
|
|
|
|
case 7: /* Noise attenuation */
|
|
{
|
|
data &= 0x0f;
|
|
SN76489.Registers[7] = data;
|
|
data = PSGVolumeValues[data];
|
|
SN76489.Channel[3][0] = (data * SN76489.PreAmp[3][0]) / 100;
|
|
SN76489.Channel[3][1] = (data * SN76489.PreAmp[3][1]) / 100;
|
|
break;
|
|
}
|
|
}
|
|
}
|