1 /***************************************************************************
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5 Routines to emulate the Texas Instruments SN76489 / SN76496 programmable
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6 tone /noise generator. Also known as (or at least compatible with) TMS9919.
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8 Noise emulation is not accurate due to lack of documentation. The noise
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9 generator uses a shift register with a XOR-feedback network, but the exact
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10 layout is unknown. It can be set for either period or white noise; again,
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11 the details are unknown.
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13 28/03/2005 : Sebastien Chevalier
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14 Update th SN76496Write func, according to SN76489 doc found on SMSPower.
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15 - On write with 0x80 set to 0, when LastRegister is other then TONE,
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16 the function is similar than update with 0x80 set to 1
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17 ***************************************************************************/
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20 #pragma warning (disable:4244)
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23 #include "sn76496.h"
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25 #define MAX_OUTPUT 0x4800 // was 0x7fff
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27 #define STEP 0x10000
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30 /* Formulas for noise generator */
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33 /* noise feedback for white noise mode (verified on real SN76489 by John Kortink) */
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34 #define FB_WNOISE_T 0x3000 /* (15bits) bit15 = bit1 ^ bit2, TI */
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35 #define FB_WNOISE_S 0x9000 /* (16bits) bit16 = bit0 ^ bit3, Sega PSG */
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37 /* noise feedback for periodic noise mode */
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38 #define FB_PNOISE_T 0x4000 /* 15bit rotate for TI */
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39 #define FB_PNOISE_S 0x8000 /* 16bit rotate for Sega PSG */
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41 #define FB_WNOISE FB_WNOISE_S /* Sega */
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42 #define FB_PNOISE FB_PNOISE_S
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47 //sound_stream * Channel;
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49 unsigned int UpdateStep;
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50 int VolTable[16]; /* volume table */
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51 int Register[8]; /* registers */
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52 int LastRegister; /* last register written */
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53 int Volume[4]; /* volume of voice 0-2 and noise */
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54 unsigned int RNG; /* noise generator */
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55 int NoiseFB; /* noise feedback mask */
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62 static struct SN76496 ono_sn; // one and only SN76496
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63 int *sn76496_regs = ono_sn.Register;
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66 void SN76496Write(int data)
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68 struct SN76496 *R = &ono_sn;
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71 /* update the output buffer before changing the registers */
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72 //stream_update(R->Channel,0);
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74 r = R->LastRegister;
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76 r = R->LastRegister = (data & 0x70) >> 4;
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79 if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))
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80 // data byte (tone only)
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81 R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
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83 R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
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85 data = R->Register[r];
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88 case 0: /* tone 0 : frequency */
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89 case 2: /* tone 1 : frequency */
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90 case 4: /* tone 2 : frequency */
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91 R->Period[c] = R->UpdateStep * data;
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92 if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
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93 if (R->Count[c] > R->Period[c]) R->Count[c] = R->Period[c];
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96 /* update noise shift frequency */
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97 if ((R->Register[6] & 0x03) == 0x03)
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98 R->Period[3] = 2 * R->Period[2];
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101 case 1: /* tone 0 : volume */
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102 case 3: /* tone 1 : volume */
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103 case 5: /* tone 2 : volume */
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104 case 7: /* noise : volume */
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105 R->Volume[c] = R->VolTable[data & 0x0f];
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107 case 6: /* noise : frequency, mode */
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109 R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
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111 /* N/512,N/1024,N/2048,Tone #3 output */
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112 R->Period[3] = 2 * (n == 3 ? R->Period[2] : R->UpdateStep << (4 + n));
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114 /* reset noise shifter */
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115 R->RNG = FB_PNOISE;
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116 R->Output[3] = R->RNG & 1;
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122 WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }
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123 WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }
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124 WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }
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125 WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }
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126 WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }
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130 void SN76496Update(short *buffer, int length, int stereo)
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133 struct SN76496 *R = &ono_sn;
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141 /* vol[] keeps track of how long each square wave stays */
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142 /* in the 1 position during the sample period. */
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143 vol[0] = vol[1] = vol[2] = vol[3] = 0;
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145 for (i = 0;i < 3;i++)
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147 if (R->Output[i]) vol[i] += R->Count[i];
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148 R->Count[i] -= STEP;
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149 /* Period[i] is the half period of the square wave. Here, in each */
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150 /* loop I add Period[i] twice, so that at the end of the loop the */
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151 /* square wave is in the same status (0 or 1) it was at the start. */
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152 /* vol[i] is also incremented by Period[i], since the wave has been 1 */
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153 /* exactly half of the time, regardless of the initial position. */
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154 /* If we exit the loop in the middle, Output[i] has to be inverted */
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155 /* and vol[i] incremented only if the exit status of the square */
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157 if (R->Count[i] < -2*R->Period[i] || R->Volume[i] == 0) {
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158 /* Cut off anything above the Nyquist frequency. */
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159 /* It will only create aliasing anyway. This is actually an */
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160 /* ideal lowpass filter with Nyquist corner frequency. */
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161 vol[i] += STEP/2; // mean value
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162 R->Count[i] = R->Output[i] = 0;
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164 while (R->Count[i] < 0)
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166 R->Count[i] += R->Period[i];
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167 if (R->Count[i] >= 0)
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170 if (R->Output[i]) vol[i] += R->Period[i];
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173 R->Count[i] += R->Period[i];
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174 vol[i] += R->Period[i];
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176 if (R->Output[i]) vol[i] -= R->Count[i];
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180 if (R->Output[3]) vol[3] += R->Count[3];
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185 if (R->Count[3] < left) nextevent = R->Count[3];
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186 else nextevent = left;
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188 R->Count[3] -= nextevent;
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189 if (R->Count[3] <= 0)
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191 R->Output[3] = R->RNG & 1;
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195 R->RNG ^= R->NoiseFB;
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196 vol[3] += R->Period[3];
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198 R->Count[3] += R->Period[3];
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202 } while (left > 0 && R->Volume[3]);
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203 if (R->Output[3]) vol[3] -= R->Count[3];
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206 if (R->Panning == 0xff || !stereo) {
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208 vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +
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209 vol[2] * R->Volume[2] + vol[3] * R->Volume[3];
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211 if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;
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213 out /= STEP; // will be optimized to shift; max 0x4800 = 18432
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215 if (stereo) *buffer++ += out;
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217 #define P(n) !!(R->Panning & (1<<(n)))
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218 unsigned int outl =
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219 vol[0] * R->Volume[0] * P(4) + vol[1] * R->Volume[1] * P(5) +
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220 vol[2] * R->Volume[2] * P(6) + vol[3] * R->Volume[3] * P(7);
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221 unsigned int outr =
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222 vol[0] * R->Volume[0] * P(0) + vol[1] * R->Volume[1] * P(1) +
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223 vol[2] * R->Volume[2] * P(2) + vol[3] * R->Volume[3] * P(3);
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225 if (outl > MAX_OUTPUT * STEP) outl = MAX_OUTPUT * STEP;
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226 if (outr > MAX_OUTPUT * STEP) outr = MAX_OUTPUT * STEP;
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228 outl /= STEP; // will be optimized to shift; max 0x4800 = 18432
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229 outr /= STEP; // will be optimized to shift; max 0x4800 = 18432
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236 void SN76496Config(int panning)
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238 struct SN76496 *R = &ono_sn;
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239 R->Panning = panning & 0xff;
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243 static void SN76496_set_clock(struct SN76496 *R,int clock)
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246 /* the base clock for the tone generators is the chip clock divided by 16; */
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247 /* for the noise generator, it is clock / 256. */
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248 /* Here we calculate the number of steps which happen during one sample */
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249 /* at the given sample rate. No. of events = sample rate / (clock/16). */
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250 /* STEP is a multiplier used to turn the fraction into a fixed point */
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252 R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;
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256 static void SN76496_set_gain(struct SN76496 *R,int gain)
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264 /* increase max output basing on gain (0.2 dB per step) */
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265 out = MAX_OUTPUT / 4.0;
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267 out *= 1.023292992; /* = (10 ^ (0.2/20)) */
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269 /* build volume table (2dB per step) */
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270 for (i = 0;i < 15;i++)
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272 /* limit volume to avoid clipping */
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273 if (out > MAX_OUTPUT / 4) R->VolTable[i] = MAX_OUTPUT / 4;
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274 else R->VolTable[i] = out;
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276 out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
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278 R->VolTable[15] = 0;
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283 void SN76496_set_clockrate(int clock,int sample_rate)
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285 struct SN76496 *R = &ono_sn;
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287 R->SampleRate = sample_rate;
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288 SN76496_set_clock(R,clock);
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292 int SN76496_init(int clock,int sample_rate)
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294 struct SN76496 *R = &ono_sn;
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297 //R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);
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299 SN76496_set_clockrate(clock,sample_rate);
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301 for (i = 0;i < 4;i++) R->Volume[i] = 0;
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303 R->LastRegister = 0;
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304 for (i = 0;i < 8;i+=2)
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306 R->Register[i] = 0;
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307 R->Register[i + 1] = 0x0f; /* volume = 0 */
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310 for (i = 0;i < 4;i++)
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312 R->Volume[i] = R->Output[i] = R->Count[i] = 0;
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313 R->Period[i] = R->UpdateStep;
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315 R->RNG = FB_PNOISE;
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316 R->Output[3] = R->RNG & 1;
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319 SN76496_set_gain(R, 0);
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