The-Homebrew-Cloud/Genesis-Plus-GX
2
0
Fork 0
mirror of https://github.com/ekeeke/Genesis-Plus-GX.git synced 2024-12-27 19:51:48 +01:00
Code Issues Packages Projects Releases Wiki Activity
41285e1131
Genesis-Plus-GX/core/sound/sn76489.c

419 lines
12 KiB
C
Raw Blame History

/*
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
04/11/16 Eke-Eke (Genesis Plus GX)
- improved resampling quality (removes aliasing noise when using high frequency tones)
- removed cut-off value (improves emulation accuracy of highest frequency tones)
- modified channels output to 0/1 like real chip instead of -1/+1 (fixes PCM voices when cut-off value is removed)
*/
#include "shared.h"
#define PSG_MCYCLES_RATIO (16 * 15)
/* Initial state of shift register */
#define NoiseInitialState 0x8000
/* 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;
void SN76489_Init(int type)
{
int i;
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)
{
/* left & right output */
int delta_l = (SN76489.Channel[i][0] * SN76489.ToneFreqPos[i]) - SN76489.ChanOut[i][0];
int delta_r = (SN76489.Channel[i][1] * SN76489.ToneFreqPos[i]) - SN76489.ChanOut[i][1];
blip_add_delta(snd.blips[0], time, delta_l, delta_r);
SN76489.ChanOut[i][0] += delta_l;
SN76489.ChanOut[i][1] += delta_r;
}
/* Updates noise amplitude in delta buffer. Call whenever amplitude might have changed. */
INLINE void UpdateNoiseAmplitude(int time)
{
/* left & right output */
int delta_l = (SN76489.Channel[3][0] * ( SN76489.NoiseShiftRegister & 0x1 )) - SN76489.ChanOut[3][0];
int delta_r = (SN76489.Channel[3][1] * ( SN76489.NoiseShiftRegister & 0x1 )) - SN76489.ChanOut[3][1];
blip_add_delta(snd.blips[0], time, delta_l, delta_r);
SN76489.ChanOut[3][0] += delta_l;
SN76489.ChanOut[3][1] += delta_r;
}
/* 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)
{
/* Flip the flip-flop */
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] ^= 1;
if (SN76489.ToneFreqPos[3])
{
/* 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 (applied to all channels) */
SN76489.PreAmp[i][0] = SN76489.PreAmp[i][0] << boostNoise;
SN76489.PreAmp[i][1] = SN76489.PreAmp[i][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;
}
}
}
Reference in New Issue View Git Blame Copy Permalink