/***************************************************************************
sn76496.c
Routines to emulate the Texas Instruments SN76489 / SN76496 programmable
tone /noise generator. Also known as (or at least compatible with) TMS9919.
Noise emulation is not accurate due to lack of documentation. The noise
generator uses a shift register with a XOR-feedback network, but the exact
layout is unknown. It can be set for either period or white noise; again,
the details are unknown.
***************************************************************************/
#include <stdint.h>
#include <string.h>
#include "system.h"
#include "sn76496.h"
#define MAX_OUTPUT 0x7fff
#define AUDIO_CONV(A) (A)
#define STEP 0x10000
/* Formulas for noise generator */
/* bit0 = output */
/* noise feedback for white noise mode */
#define FB_WNOISE 0x12000 /* bit15.d(16bits) = bit0(out) ^ bit2 */
//#define FB_WNOISE 0x14000 /* bit15.d(16bits) = bit0(out) ^ bit1 */
//#define FB_WNOISE 0x28000 /* bit16.d(17bits) = bit0(out) ^ bit2 (same to AY-3-8910) */
//#define FB_WNOISE 0x50000 /* bit17.d(18bits) = bit0(out) ^ bit2 */
/* noise feedback for periodic noise mode */
/* it is correct maybe (it was in the Megadrive sound manual) */
//#define FB_PNOISE 0x10000 /* 16bit rorate */
#define FB_PNOISE 0x08000 /* JH 981127 - fixes Do Run Run */
/* noise generator start preset (for periodic noise) */
#define NG_PRESET 0x0f35
struct SN76496
{
int Channel;
int SampleRate;
unsigned int UpdateStep;
int VolTable[16]; /* volume table */
int Register[8]; /* registers */
int LastRegister; /* last register written */
int Volume[4]; /* volume of voice 0-2 and noise */
unsigned int RNG; /* noise generator */
int NoiseFB; /* noise feedback mask */
unsigned int Period[4];
int Count[4];
int Output[4];
};
static struct SN76496 sn[MAX_76496];
void SN76496_dump(int chip, uint8_t buf[16])
{
struct SN76496 *R = &sn[chip];
uint16_t tmp;
unsigned int i;
for (i = 0; (i < 8); ++i) {
tmp = h2le16(R->Register[i]);
memcpy(&buf
[(i
* 2)], &tmp
, 2); }
}
void SN76496_restore(int chip, uint8_t buf[16])
{
struct SN76496 *R = &sn[chip];
uint16_t tmp;
unsigned int i;
for (i = 0; (i < 8); ++i) {
memcpy(&tmp
, &buf
[(i
* 2)], 2); R->Register[i] = le2h16(tmp);
}
}
void SN76496Write(int chip,int data)
{
struct SN76496 *R = &sn[chip];
/* update the output buffer before changing the registers */
///// commented out by starshine
//stream_update(R->Channel,0);
if (data & 0x80)
{
int r = (data & 0x70) >> 4;
int c = r/2;
R->LastRegister = r;
R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
switch (r)
{
case 0: /* tone 0 : frequency */
case 2: /* tone 1 : frequency */
case 4: /* tone 2 : frequency */
R->Period[c] = R->UpdateStep * R->Register[r];
if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
if (r == 4)
{
/* update noise shift frequency */
if ((R->Register[6] & 0x03) == 0x03)
R->Period[3] = 2 * R->Period[2];
}
break;
case 1: /* tone 0 : volume */
case 3: /* tone 1 : volume */
case 5: /* tone 2 : volume */
case 7: /* noise : volume */
R->Volume[c] = R->VolTable[data & 0x0f];
break;
case 6: /* noise : frequency, mode */
{
int n = R->Register[6];
R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
n &= 3;
/* N/512,N/1024,N/2048,Tone #3 output */
R->Period[3] = (n == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+n));
/* reset noise shifter */
R->RNG = NG_PRESET;
R->Output[3] = R->RNG & 1;
}
break;
}
}
else
{
int r = R->LastRegister;
int c = r/2;
switch (r)
{
case 0: /* tone 0 : frequency */
case 2: /* tone 1 : frequency */
case 4: /* tone 2 : frequency */
R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
R->Period[c] = R->UpdateStep * R->Register[r];
if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
if (r == 4)
{
/* update noise shift frequency */
if ((R->Register[6] & 0x03) == 0x03)
R->Period[3] = 2 * R->Period[2];
}
break;
}
}
}
void SN76496_0_w(int offset, int data) { (void)offset; SN76496Write(0, data); }
void SN76496_1_w(int offset, int data) { (void)offset; SN76496Write(1, data); }
void SN76496_2_w(int offset, int data) { (void)offset; SN76496Write(2, data); }
void SN76496_3_w(int offset, int data) { (void)offset; SN76496Write(3, data); }
void SN76496Update_8_2(int chip,void *buffer,int length)
{
#define DATATYPE unsigned char
#define DATACONV(A) AUDIO_CONV((A) / (STEP * 256))
#include "sn76496u.c"
#undef DATATYPE
#undef DATACONV
}
void SN76496Update_16_2(int chip,void *buffer,int length)
{
#define DATATYPE unsigned short
#define DATACONV(A) ((A) / STEP)
#include "sn76496u.c"
#undef DATATYPE
#undef DATACONV
}
void SN76496_set_clock
(int chip
,int clock) {
struct SN76496 *R = &sn[chip];
/* the base clock for the tone generators is the chip clock divided by 16; */
/* for the noise generator, it is clock / 256. */
/* Here we calculate the number of steps which happen during one sample */
/* at the given sample rate. No. of events = sample rate / (clock/16). */
/* STEP is a multiplier used to turn the fraction into a fixed point */
/* number. */
R
->UpdateStep
= ((double)STEP
* R
->SampleRate
* 16) / clock;}
static void SN76496_set_volume(int chip,int volume,int gain)
{
struct SN76496 *R = &sn[chip];
int i;
double out;
(void)volume;
///// commented out by starshine
//stream_set_volume(R->Channel,volume);
gain &= 0xff;
/* increase max output basing on gain (0.2 dB per step) */
out = MAX_OUTPUT / 3;
while (gain-- > 0)
out *= 1.023292992; /* = (10 ^ (0.2/20)) */
/* build volume table (2dB per step) */
for (i = 0;i < 15;i++)
{
/* limit volume to avoid clipping */
if (out > MAX_OUTPUT / 3) R->VolTable[i] = MAX_OUTPUT / 3;
else R->VolTable[i] = out;
out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
}
R->VolTable[15] = 0;
}
int SN76496_init
(int chip
,int clock,int sample_rate
,int sample_bits
) {
int i;
struct SN76496 *R = &sn[chip];
/* char name[40]; */
(void)sample_bits;
////// commented out by starshine
//sprintf(name,"SN76496 #%d",chip);
//R->Channel = stream_init(msound,
// name,sample_rate,sample_bits,
// chip,(sample_bits == 16) ? SN76496Update_16 : SN76496Update_8);
if (R->Channel == -1)
return 1;
R->SampleRate = sample_rate;
SN76496_set_clock
(chip
,clock); SN76496_set_volume(chip,255,0);
for (i = 0;i < 4;i++) R->Volume[i] = 0;
R->LastRegister = 0;
for (i = 0;i < 8;i+=2)
{
R->Register[i] = 0;
R->Register[i + 1] = 0x0f; /* volume = 0 */
}
for (i = 0;i < 4;i++)
{
R->Output[i] = 0;
R->Period[i] = R->Count[i] = R->UpdateStep;
}
R->RNG = NG_PRESET;
R->Output[3] = R->RNG & 1;
return 0;
}
int SN76496_sh_start()
{
///// total commenting out by starshine
//int chip;
//const struct SN76496interface *intf = msound->sound_interface;
//for (chip = 0;chip < intf->num;chip++)
//{
// if (SN76496_init(msound,chip,intf->baseclock,Machine->sample_rate,Machine->sample_bits) != 0)
// return 1;
// SN76496_set_volume(chip,intf->volume[chip] & 0xff,(intf->volume[chip] >> 8) & 0xff);
//}
return 0;
}