mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-05 02:15:07 +01:00
312 lines
7.1 KiB
C
312 lines
7.1 KiB
C
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#include "shared.h"
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#define MAX_OUTPUT 0x7fff
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#define STEP 0x10000
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#define FB_WNOISE 0x14002
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#define FB_PNOISE 0x08000
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#define NG_PRESET 0x0F35
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struct SN76496 sn[MAX_76496];
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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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int n;
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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)
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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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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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/*
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* Amended from Mame 1.04s
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*
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* R->Period[3] = (n == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+n));
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*/
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R->Period[3] =
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((n & 3) ==
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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)
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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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* Additions from Mame 1.04
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* Start Here
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*/
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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] =
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((n & 3) ==
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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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void SN76496Update (int chip, signed short int *buffer, int length)
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{
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int i;
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struct SN76496 *R = &sn[chip];
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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)
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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])
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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])
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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])
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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)
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nextevent = R->Count[3];
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else
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nextevent = left;
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if (R->Output[3])
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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)
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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])
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vol[3] += R->Period[3];
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}
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if (R->Output[3])
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vol[3] -= R->Count[3];
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left -= nextevent;
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}
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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)
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out = MAX_OUTPUT * STEP;
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*(buffer++) = out / STEP;
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length--;
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}
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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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void SN76496_set_gain (int chip, 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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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)
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R->VolTable[i] = MAX_OUTPUT / 3;
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else
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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 volume, int sample_rate)
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{
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int i;
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struct SN76496 *R = &sn[chip];
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R->SampleRate = sample_rate;
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SN76496_set_clock (chip, clock);
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for (i = 0; i < 4; i++)
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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 (int clock, int volume, int rate)
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{
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SN76496_init (0, clock, volume & 0xff, rate);
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SN76496_set_gain (0, (volume >> 8) & 0xff);
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return 0;
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}
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