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