345 lines
9.3 KiB
C
345 lines
9.3 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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28/03/2005 : Sebastien Chevalier
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Update th SN76496Write func, according to SN76489 doc found on SMSPower.
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- On write with 0x80 set to 0, when LastRegister is other then TONE,
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the function is similar than update with 0x80 set to 1
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***************************************************************************/
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#ifndef __GNUC__
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#pragma warning (disable:4244)
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#endif
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#include "sn76496.h"
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#define MAX_OUTPUT 0x47ff // was 0x7fff
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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 (verified on real SN76489 by John Kortink) */
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#define FB_WNOISE 0x14002 /* (16bits) bit16 = bit0(out) ^ bit2 ^ bit15 */
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/* noise feedback for periodic noise mode */
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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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/*
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0x08000 is definitely wrong. The Master System conversion of Marble Madness
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uses periodic noise as a baseline. With a 15-bit rotate, the bassline is
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out of tune.
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The 16-bit rotate has been confirmed against a real PAL Sega Master System 2.
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Hope that helps the System E stuff, more news on the PSG as and when!
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*/
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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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//sound_stream * 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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int Period[4];
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int Count[4];
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int Output[4];
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int pad[1];
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};
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static struct SN76496 ono_sn; // one and only SN76496
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int *sn76496_regs;
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//static
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void SN76496Write(int data)
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{
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struct SN76496 *R = &ono_sn;
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int n;
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/* update the output buffer before changing the registers */
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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) == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+(n&3)));
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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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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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R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
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break;
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case 6: /* noise : frequency, mode */
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{
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R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
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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) == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+(n&3)));
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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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}
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/*
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WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }
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WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }
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WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }
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WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }
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WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }
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*/
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//static
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void SN76496Update(short *buffer, int length, int stereo)
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{
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int i;
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struct SN76496 *R = &ono_sn;
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/* If the volume is 0, increase the counter */
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for (i = 0;i < 4;i++)
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{
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if (R->Volume[i] == 0)
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{
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/* note that I do count += length, NOT count = length + 1. You might think */
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/* it's the same since the volume is 0, but doing the latter could cause */
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/* interferencies when the program is rapidly modulating the volume. */
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if (R->Count[i] <= length*STEP) R->Count[i] += length*STEP;
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}
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}
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while (length > 0)
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{
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int vol[4];
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unsigned int out;
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int left;
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/* vol[] keeps track of how long each square wave stays */
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/* in the 1 position during the sample period. */
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vol[0] = vol[1] = vol[2] = vol[3] = 0;
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for (i = 0;i < 3;i++)
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{
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if (R->Output[i]) vol[i] += R->Count[i];
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R->Count[i] -= STEP;
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/* Period[i] is the half period of the square wave. Here, in each */
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/* loop I add Period[i] twice, so that at the end of the loop the */
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/* square wave is in the same status (0 or 1) it was at the start. */
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/* vol[i] is also incremented by Period[i], since the wave has been 1 */
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/* exactly half of the time, regardless of the initial position. */
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/* If we exit the loop in the middle, Output[i] has to be inverted */
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/* and vol[i] incremented only if the exit status of the square */
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/* wave is 1. */
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while (R->Count[i] <= 0)
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{
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R->Count[i] += R->Period[i];
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if (R->Count[i] > 0)
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{
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R->Output[i] ^= 1;
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if (R->Output[i]) vol[i] += R->Period[i];
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break;
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}
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R->Count[i] += R->Period[i];
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vol[i] += R->Period[i];
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}
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if (R->Output[i]) vol[i] -= R->Count[i];
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}
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left = STEP;
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do
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{
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int nextevent;
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if (R->Count[3] < left) nextevent = R->Count[3];
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else nextevent = left;
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if (R->Output[3]) vol[3] += R->Count[3];
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R->Count[3] -= nextevent;
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if (R->Count[3] <= 0)
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{
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if (R->RNG & 1) R->RNG ^= R->NoiseFB;
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R->RNG >>= 1;
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R->Output[3] = R->RNG & 1;
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R->Count[3] += R->Period[3];
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if (R->Output[3]) vol[3] += R->Period[3];
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}
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if (R->Output[3]) vol[3] -= R->Count[3];
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left -= nextevent;
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} while (left > 0);
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out = vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +
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vol[2] * R->Volume[2] + vol[3] * R->Volume[3];
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if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;
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if ((out /= STEP)) // will be optimized to shift; max 0x47ff = 18431
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*buffer += out;
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if(stereo) buffer+=2; // only left for stereo, to be mixed to right later
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else buffer++;
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length--;
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}
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}
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static void SN76496_set_clock(struct SN76496 *R,int clock)
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{
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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_gain(struct SN76496 *R,int gain)
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{
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int i;
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double out;
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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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//static
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int SN76496_init(int clock,int sample_rate)
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{
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struct SN76496 *R = &ono_sn;
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int i;
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//R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);
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sn76496_regs = R->Register;
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R->SampleRate = sample_rate;
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SN76496_set_clock(R,clock);
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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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// added
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SN76496_set_gain(R, 0);
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return 0;
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}
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