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- /***************************************************************************
- 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.
- 28/03/2005 : Sebastien Chevalier
- Update th SN76496Write func, according to SN76489 doc found on SMSPower.
- - On write with 0x80 set to 0, when LastRegister is other then TONE,
- the function is similar than update with 0x80 set to 1
- ***************************************************************************/
- #ifndef __GNUC__
- #pragma warning (disable:4244)
- #endif
- #include "sn76496.h"
- #define MAX_OUTPUT 0x4800 // was 0x7fff
- #define STEP 0x10000
- /* Formulas for noise generator */
- /* bit0 = output */
- /* noise feedback for white noise mode (verified on real SN76489 by John Kortink) */
- #define FB_WNOISE_T 0x3000 /* (15bits) bit15 = bit1 ^ bit2, TI */
- #define FB_WNOISE_S 0x9000 /* (16bits) bit16 = bit0 ^ bit3, Sega PSG */
- /* noise feedback for periodic noise mode */
- #define FB_PNOISE_T 0x4000 /* 15bit rotate for TI */
- #define FB_PNOISE_S 0x8000 /* 16bit rotate for Sega PSG */
- #define FB_WNOISE FB_WNOISE_S /* Sega */
- #define FB_PNOISE FB_PNOISE_S
- struct SN76496
- {
- //sound_stream * 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 */
- int Period[4];
- int Count[4];
- int Output[4];
- int pad[1];
- };
- static struct SN76496 ono_sn; // one and only SN76496
- int *sn76496_regs;
- //static
- void SN76496Write(int data)
- {
- struct SN76496 *R = &ono_sn;
- int n, r, c;
- /* update the output buffer before changing the registers */
- //stream_update(R->Channel,0);
- r = R->LastRegister;
- if (data & 0x80)
- r = R->LastRegister = (data & 0x70) >> 4;
- c = r / 2;
- if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))
- // data byte (tone only)
- R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
- else
- R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
- data = R->Register[r];
- switch (r)
- {
- case 0: /* tone 0 : frequency */
- case 2: /* tone 1 : frequency */
- case 4: /* tone 2 : frequency */
- R->Period[c] = R->UpdateStep * data;
- if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
- if (R->Count[c] > R->Period[c]) R->Count[c] = R->Period[c];
- 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 */
- n = data;
- R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
- n &= 3;
- /* N/512,N/1024,N/2048,Tone #3 output */
- R->Period[3] = 2 * (n == 3 ? R->Period[2] : R->UpdateStep << (4 + n));
- /* reset noise shifter */
- R->RNG = FB_PNOISE;
- R->Output[3] = R->RNG & 1;
- break;
- }
- }
- /*
- WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }
- WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }
- WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }
- WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }
- WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }
- */
- //static
- void SN76496Update(short *buffer, int length, int stereo)
- {
- int i;
- struct SN76496 *R = &ono_sn;
- while (length > 0)
- {
- int vol[4];
- unsigned int out;
- int left;
- /* vol[] keeps track of how long each square wave stays */
- /* in the 1 position during the sample period. */
- vol[0] = vol[1] = vol[2] = vol[3] = 0;
- for (i = 0;i < 3;i++)
- {
- if (R->Output[i]) vol[i] += R->Count[i];
- R->Count[i] -= STEP;
- /* Period[i] is the half period of the square wave. Here, in each */
- /* loop I add Period[i] twice, so that at the end of the loop the */
- /* square wave is in the same status (0 or 1) it was at the start. */
- /* vol[i] is also incremented by Period[i], since the wave has been 1 */
- /* exactly half of the time, regardless of the initial position. */
- /* If we exit the loop in the middle, Output[i] has to be inverted */
- /* and vol[i] incremented only if the exit status of the square */
- /* wave is 1. */
- if (R->Count[i] < -2*R->Period[i] || R->Volume[i] == 0) {
- /* Cut off anything above the Nyquist frequency. */
- /* It will only create aliasing anyway. This is actually an */
- /* ideal lowpass filter with Nyquist corner frequency. */
- vol[i] += STEP/2; // mean value
- R->Count[i] = R->Output[i] = 0;
- }
- while (R->Count[i] < 0)
- {
- R->Count[i] += R->Period[i];
- if (R->Count[i] >= 0)
- {
- R->Output[i] ^= 1;
- if (R->Output[i]) vol[i] += R->Period[i];
- break;
- }
- R->Count[i] += R->Period[i];
- vol[i] += R->Period[i];
- }
- if (R->Output[i]) vol[i] -= R->Count[i];
- }
- left = STEP;
- if (R->Output[3]) vol[3] += R->Count[3];
- do
- {
- int nextevent;
- if (R->Count[3] < left) nextevent = R->Count[3];
- else nextevent = left;
- R->Count[3] -= nextevent;
- if (R->Count[3] <= 0)
- {
- R->Output[3] = R->RNG & 1;
- R->RNG >>= 1;
- if (R->Output[3])
- {
- R->RNG ^= R->NoiseFB;
- vol[3] += R->Period[3];
- }
- R->Count[3] += R->Period[3];
- }
- left -= nextevent;
- } while (left > 0 && R->Volume[3]);
- if (R->Output[3]) vol[3] -= R->Count[3];
- out = vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +
- vol[2] * R->Volume[2] + vol[3] * R->Volume[3];
- if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;
- if ((out /= STEP)) // will be optimized to shift; max 0x4800 = 18432
- *buffer += out;
- if(stereo) buffer+=2; // only left for stereo, to be mixed to right later
- else buffer++;
- length--;
- }
- }
- static void SN76496_set_clock(struct SN76496 *R,int clock)
- {
- /* 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_gain(struct SN76496 *R,int gain)
- {
- int i;
- double out;
- gain &= 0xff;
- /* increase max output basing on gain (0.2 dB per step) */
- out = MAX_OUTPUT / 4.0;
- 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 / 4) R->VolTable[i] = MAX_OUTPUT / 4;
- else R->VolTable[i] = out;
- out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
- }
- R->VolTable[15] = 0;
- }
- //static
- int SN76496_init(int clock,int sample_rate)
- {
- struct SN76496 *R = &ono_sn;
- int i;
- //R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);
- sn76496_regs = R->Register;
- R->SampleRate = sample_rate;
- SN76496_set_clock(R,clock);
- 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->Volume[i] = R->Output[i] = R->Count[i] = 0;
- R->Period[i] = R->UpdateStep;
- }
- R->RNG = FB_PNOISE;
- R->Output[3] = R->RNG & 1;
- // added
- SN76496_set_gain(R, 0);
- return 0;
- }
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