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1 | /***************************************************************************\r |
2 | \r |
3 | sn76496.c\r |
4 | \r |
5 | Routines to emulate the Texas Instruments SN76489 / SN76496 programmable\r |
6 | tone /noise generator. Also known as (or at least compatible with) TMS9919.\r |
7 | \r |
8 | Noise emulation is not accurate due to lack of documentation. The noise\r |
9 | generator uses a shift register with a XOR-feedback network, but the exact\r |
10 | layout is unknown. It can be set for either period or white noise; again,\r |
11 | the details are unknown.\r |
12 | \r |
13 | 28/03/2005 : Sebastien Chevalier\r |
14 | Update th SN76496Write func, according to SN76489 doc found on SMSPower.\r |
15 | - On write with 0x80 set to 0, when LastRegister is other then TONE,\r |
16 | the function is similar than update with 0x80 set to 1\r |
17 | ***************************************************************************/\r |
18 | \r |
19 | #ifndef __GNUC__\r |
20 | #pragma warning (disable:4244)\r |
21 | #endif\r |
22 | \r |
23 | #include "sn76496.h"\r |
24 | \r |
af01b1b1 |
25 | #define MAX_OUTPUT 0x4800 // was 0x7fff\r |
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26 | \r |
27 | #define STEP 0x10000\r |
28 | \r |
29 | \r |
30 | /* Formulas for noise generator */\r |
31 | /* bit0 = output */\r |
32 | \r |
33 | /* noise feedback for white noise mode (verified on real SN76489 by John Kortink) */\r |
af01b1b1 |
34 | #define FB_WNOISE_T 0x3000 /* (15bits) bit15 = bit1 ^ bit2, TI */\r |
35 | #define FB_WNOISE_S 0x9000 /* (16bits) bit16 = bit0 ^ bit3, Sega PSG */\r |
cc68a136 |
36 | \r |
37 | /* noise feedback for periodic noise mode */\r |
af01b1b1 |
38 | #define FB_PNOISE_T 0x4000 /* 15bit rotate for TI */\r |
39 | #define FB_PNOISE_S 0x8000 /* 16bit rotate for Sega PSG */\r |
cc68a136 |
40 | \r |
af01b1b1 |
41 | #define FB_WNOISE FB_WNOISE_S /* Sega */\r |
42 | #define FB_PNOISE FB_PNOISE_S\r |
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43 | \r |
44 | \r |
45 | struct SN76496\r |
46 | {\r |
47 | //sound_stream * Channel;\r |
48 | int SampleRate;\r |
49 | unsigned int UpdateStep;\r |
50 | int VolTable[16]; /* volume table */\r |
51 | int Register[8]; /* registers */\r |
52 | int LastRegister; /* last register written */\r |
53 | int Volume[4]; /* volume of voice 0-2 and noise */\r |
af01b1b1 |
54 | unsigned int RNG; /* noise generator */\r |
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55 | int NoiseFB; /* noise feedback mask */\r |
56 | int Period[4];\r |
57 | int Count[4];\r |
58 | int Output[4];\r |
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59 | int Panning;\r |
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60 | };\r |
61 | \r |
62 | static struct SN76496 ono_sn; // one and only SN76496\r |
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63 | int *sn76496_regs = ono_sn.Register;\r |
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64 | \r |
65 | //static\r |
66 | void SN76496Write(int data)\r |
67 | {\r |
68 | struct SN76496 *R = &ono_sn;\r |
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69 | int n, r, c;\r |
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70 | \r |
71 | /* update the output buffer before changing the registers */\r |
72 | //stream_update(R->Channel,0);\r |
73 | \r |
5103774f |
74 | r = R->LastRegister;\r |
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75 | if (data & 0x80)\r |
5103774f |
76 | r = R->LastRegister = (data & 0x70) >> 4;\r |
77 | c = r / 2;\r |
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78 | \r |
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79 | if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))\r |
80 | // data byte (tone only)\r |
81 | R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);\r |
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82 | else\r |
5103774f |
83 | R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);\r |
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84 | \r |
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85 | data = R->Register[r];\r |
86 | switch (r)\r |
87 | {\r |
88 | case 0: /* tone 0 : frequency */\r |
89 | case 2: /* tone 1 : frequency */\r |
90 | case 4: /* tone 2 : frequency */\r |
91 | R->Period[c] = R->UpdateStep * data;\r |
92 | if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;\r |
6985cdd8 |
93 | if (R->Count[c] > R->Period[c]) R->Count[c] = R->Period[c];\r |
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94 | if (r == 4)\r |
95 | {\r |
96 | /* update noise shift frequency */\r |
97 | if ((R->Register[6] & 0x03) == 0x03)\r |
98 | R->Period[3] = 2 * R->Period[2];\r |
99 | }\r |
100 | break;\r |
101 | case 1: /* tone 0 : volume */\r |
102 | case 3: /* tone 1 : volume */\r |
103 | case 5: /* tone 2 : volume */\r |
104 | case 7: /* noise : volume */\r |
105 | R->Volume[c] = R->VolTable[data & 0x0f];\r |
106 | break;\r |
107 | case 6: /* noise : frequency, mode */\r |
108 | n = data;\r |
109 | R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;\r |
110 | n &= 3;\r |
111 | /* N/512,N/1024,N/2048,Tone #3 output */\r |
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112 | R->Period[3] = 2 * (n == 3 ? R->Period[2] : R->UpdateStep << (4 + n));\r |
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113 | \r |
114 | /* reset noise shifter */\r |
af01b1b1 |
115 | R->RNG = FB_PNOISE;\r |
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116 | R->Output[3] = R->RNG & 1;\r |
117 | break;\r |
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118 | }\r |
119 | }\r |
120 | \r |
121 | /*\r |
122 | WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }\r |
123 | WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }\r |
124 | WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }\r |
125 | WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }\r |
126 | WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }\r |
127 | */\r |
128 | \r |
129 | //static\r |
4f265db7 |
130 | void SN76496Update(short *buffer, int length, int stereo)\r |
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131 | {\r |
132 | int i;\r |
133 | struct SN76496 *R = &ono_sn;\r |
134 | \r |
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135 | while (length > 0)\r |
136 | {\r |
137 | int vol[4];\r |
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138 | int left;\r |
139 | \r |
140 | \r |
141 | /* vol[] keeps track of how long each square wave stays */\r |
142 | /* in the 1 position during the sample period. */\r |
143 | vol[0] = vol[1] = vol[2] = vol[3] = 0;\r |
144 | \r |
145 | for (i = 0;i < 3;i++)\r |
146 | {\r |
147 | if (R->Output[i]) vol[i] += R->Count[i];\r |
148 | R->Count[i] -= STEP;\r |
149 | /* Period[i] is the half period of the square wave. Here, in each */\r |
150 | /* loop I add Period[i] twice, so that at the end of the loop the */\r |
151 | /* square wave is in the same status (0 or 1) it was at the start. */\r |
152 | /* vol[i] is also incremented by Period[i], since the wave has been 1 */\r |
153 | /* exactly half of the time, regardless of the initial position. */\r |
154 | /* If we exit the loop in the middle, Output[i] has to be inverted */\r |
155 | /* and vol[i] incremented only if the exit status of the square */\r |
156 | /* wave is 1. */\r |
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157 | if (R->Count[i] < -2*R->Period[i] || R->Volume[i] == 0) {\r |
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158 | /* Cut off anything above the Nyquist frequency. */\r |
159 | /* It will only create aliasing anyway. This is actually an */\r |
160 | /* ideal lowpass filter with Nyquist corner frequency. */\r |
af01b1b1 |
161 | vol[i] += STEP/2; // mean value\r |
162 | R->Count[i] = R->Output[i] = 0;\r |
163 | }\r |
164 | while (R->Count[i] < 0)\r |
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165 | {\r |
af01b1b1 |
166 | R->Count[i] += R->Period[i];\r |
167 | if (R->Count[i] >= 0)\r |
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168 | {\r |
169 | R->Output[i] ^= 1;\r |
170 | if (R->Output[i]) vol[i] += R->Period[i];\r |
171 | break;\r |
172 | }\r |
173 | R->Count[i] += R->Period[i];\r |
174 | vol[i] += R->Period[i];\r |
175 | }\r |
176 | if (R->Output[i]) vol[i] -= R->Count[i];\r |
177 | }\r |
178 | \r |
179 | left = STEP;\r |
af01b1b1 |
180 | if (R->Output[3]) vol[3] += R->Count[3];\r |
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181 | do\r |
182 | {\r |
183 | int nextevent;\r |
184 | \r |
185 | if (R->Count[3] < left) nextevent = R->Count[3];\r |
186 | else nextevent = left;\r |
187 | \r |
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188 | R->Count[3] -= nextevent;\r |
189 | if (R->Count[3] <= 0)\r |
190 | {\r |
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191 | R->Output[3] = R->RNG & 1;\r |
af01b1b1 |
192 | R->RNG >>= 1;\r |
193 | if (R->Output[3])\r |
194 | {\r |
195 | R->RNG ^= R->NoiseFB;\r |
196 | vol[3] += R->Period[3];\r |
197 | }\r |
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198 | R->Count[3] += R->Period[3];\r |
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199 | }\r |
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200 | \r |
201 | left -= nextevent;\r |
fa0c5b45 |
202 | } while (left > 0 && R->Volume[3]);\r |
af01b1b1 |
203 | if (R->Output[3]) vol[3] -= R->Count[3];\r |
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204 | \r |
70efc52d |
205 | length--;\r |
206 | if (R->Panning == 0xff || !stereo) {\r |
207 | unsigned int out =\r |
208 | vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +\r |
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209 | vol[2] * R->Volume[2] + vol[3] * R->Volume[3];\r |
210 | \r |
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211 | if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;\r |
212 | \r |
213 | out /= STEP; // will be optimized to shift; max 0x4800 = 18432\r |
214 | *buffer++ += out;\r |
215 | if (stereo) *buffer++ += out;\r |
216 | } else {\r |
217 | #define P(n) !!(R->Panning & (1<<(n)))\r |
218 | unsigned int outl =\r |
219 | vol[0] * R->Volume[0] * P(4) + vol[1] * R->Volume[1] * P(5) +\r |
220 | vol[2] * R->Volume[2] * P(6) + vol[3] * R->Volume[3] * P(7);\r |
221 | unsigned int outr =\r |
222 | vol[0] * R->Volume[0] * P(0) + vol[1] * R->Volume[1] * P(1) +\r |
223 | vol[2] * R->Volume[2] * P(2) + vol[3] * R->Volume[3] * P(3);\r |
224 | #undef P\r |
225 | if (outl > MAX_OUTPUT * STEP) outl = MAX_OUTPUT * STEP;\r |
226 | if (outr > MAX_OUTPUT * STEP) outr = MAX_OUTPUT * STEP;\r |
227 | \r |
228 | outl /= STEP; // will be optimized to shift; max 0x4800 = 18432\r |
229 | outr /= STEP; // will be optimized to shift; max 0x4800 = 18432\r |
230 | *buffer++ += outl;\r |
231 | *buffer++ += outr;\r |
232 | }\r |
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233 | }\r |
234 | }\r |
235 | \r |
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236 | void SN76496Config(int panning)\r |
237 | {\r |
238 | struct SN76496 *R = &ono_sn;\r |
239 | R->Panning = panning & 0xff;\r |
240 | }\r |
241 | \r |
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242 | \r |
243 | static void SN76496_set_clock(struct SN76496 *R,int clock)\r |
244 | {\r |
245 | \r |
246 | /* the base clock for the tone generators is the chip clock divided by 16; */\r |
247 | /* for the noise generator, it is clock / 256. */\r |
248 | /* Here we calculate the number of steps which happen during one sample */\r |
249 | /* at the given sample rate. No. of events = sample rate / (clock/16). */\r |
250 | /* STEP is a multiplier used to turn the fraction into a fixed point */\r |
251 | /* number. */\r |
252 | R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;\r |
253 | }\r |
254 | \r |
255 | \r |
256 | static void SN76496_set_gain(struct SN76496 *R,int gain)\r |
257 | {\r |
258 | int i;\r |
259 | double out;\r |
260 | \r |
261 | \r |
262 | gain &= 0xff;\r |
263 | \r |
264 | /* increase max output basing on gain (0.2 dB per step) */\r |
af01b1b1 |
265 | out = MAX_OUTPUT / 4.0;\r |
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266 | while (gain-- > 0)\r |
267 | out *= 1.023292992; /* = (10 ^ (0.2/20)) */\r |
268 | \r |
269 | /* build volume table (2dB per step) */\r |
270 | for (i = 0;i < 15;i++)\r |
271 | {\r |
272 | /* limit volume to avoid clipping */\r |
af01b1b1 |
273 | if (out > MAX_OUTPUT / 4) R->VolTable[i] = MAX_OUTPUT / 4;\r |
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274 | else R->VolTable[i] = out;\r |
275 | \r |
276 | out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */\r |
277 | }\r |
278 | R->VolTable[15] = 0;\r |
279 | }\r |
280 | \r |
281 | \r |
864ac1d6 |
282 | //static\r |
283 | void SN76496_set_clockrate(int clock,int sample_rate)\r |
284 | {\r |
285 | struct SN76496 *R = &ono_sn;\r |
286 | \r |
287 | R->SampleRate = sample_rate;\r |
288 | SN76496_set_clock(R,clock);\r |
289 | }\r |
290 | \r |
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291 | //static\r |
292 | int SN76496_init(int clock,int sample_rate)\r |
293 | {\r |
294 | struct SN76496 *R = &ono_sn;\r |
295 | int i;\r |
296 | \r |
297 | //R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);\r |
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298 | \r |
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299 | SN76496_set_clockrate(clock,sample_rate);\r |
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300 | \r |
301 | for (i = 0;i < 4;i++) R->Volume[i] = 0;\r |
302 | \r |
303 | R->LastRegister = 0;\r |
304 | for (i = 0;i < 8;i+=2)\r |
305 | {\r |
306 | R->Register[i] = 0;\r |
307 | R->Register[i + 1] = 0x0f; /* volume = 0 */\r |
308 | }\r |
309 | \r |
310 | for (i = 0;i < 4;i++)\r |
311 | {\r |
af01b1b1 |
312 | R->Volume[i] = R->Output[i] = R->Count[i] = 0;\r |
313 | R->Period[i] = R->UpdateStep;\r |
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314 | }\r |
af01b1b1 |
315 | R->RNG = FB_PNOISE;\r |
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316 | R->Output[3] = R->RNG & 1;\r |
317 | \r |
318 | // added\r |
319 | SN76496_set_gain(R, 0);\r |
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320 | R->Panning = 0xff;\r |
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321 | \r |
322 | return 0;\r |
323 | }\r |
324 | \r |