cc68a136 |
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 |
25 | #define MAX_OUTPUT 0x47ff // was 0x7fff\r |
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 |
34 | #define FB_WNOISE 0x14002 /* (16bits) bit16 = bit0(out) ^ bit2 ^ bit15 */\r |
35 | \r |
36 | /* noise feedback for periodic noise mode */\r |
37 | //#define FB_PNOISE 0x10000 /* 16bit rorate */\r |
38 | #define FB_PNOISE 0x08000 /* JH 981127 - fixes Do Run Run */\r |
39 | \r |
40 | /*\r |
41 | 0x08000 is definitely wrong. The Master System conversion of Marble Madness\r |
42 | uses periodic noise as a baseline. With a 15-bit rotate, the bassline is\r |
43 | out of tune.\r |
44 | The 16-bit rotate has been confirmed against a real PAL Sega Master System 2.\r |
45 | Hope that helps the System E stuff, more news on the PSG as and when!\r |
46 | */\r |
47 | \r |
48 | /* noise generator start preset (for periodic noise) */\r |
49 | #define NG_PRESET 0x0f35\r |
50 | \r |
51 | \r |
52 | struct SN76496\r |
53 | {\r |
54 | //sound_stream * Channel;\r |
55 | int SampleRate;\r |
56 | unsigned int UpdateStep;\r |
57 | int VolTable[16]; /* volume table */\r |
58 | int Register[8]; /* registers */\r |
59 | int LastRegister; /* last register written */\r |
60 | int Volume[4]; /* volume of voice 0-2 and noise */\r |
61 | unsigned int RNG; /* noise generator */\r |
62 | int NoiseFB; /* noise feedback mask */\r |
63 | int Period[4];\r |
64 | int Count[4];\r |
65 | int Output[4];\r |
66 | int pad[1];\r |
67 | };\r |
68 | \r |
69 | static struct SN76496 ono_sn; // one and only SN76496\r |
70 | int *sn76496_regs;\r |
71 | \r |
72 | //static\r |
73 | void SN76496Write(int data)\r |
74 | {\r |
75 | struct SN76496 *R = &ono_sn;\r |
5103774f |
76 | int n, r, c;\r |
cc68a136 |
77 | \r |
78 | /* update the output buffer before changing the registers */\r |
79 | //stream_update(R->Channel,0);\r |
80 | \r |
5103774f |
81 | r = R->LastRegister;\r |
cc68a136 |
82 | if (data & 0x80)\r |
5103774f |
83 | r = R->LastRegister = (data & 0x70) >> 4;\r |
84 | c = r / 2;\r |
cc68a136 |
85 | \r |
5103774f |
86 | if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))\r |
87 | // data byte (tone only)\r |
88 | R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);\r |
cc68a136 |
89 | else\r |
5103774f |
90 | R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);\r |
cc68a136 |
91 | \r |
5103774f |
92 | data = R->Register[r];\r |
93 | switch (r)\r |
94 | {\r |
95 | case 0: /* tone 0 : frequency */\r |
96 | case 2: /* tone 1 : frequency */\r |
97 | case 4: /* tone 2 : frequency */\r |
98 | R->Period[c] = R->UpdateStep * data;\r |
99 | if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;\r |
100 | if (r == 4)\r |
101 | {\r |
102 | /* update noise shift frequency */\r |
103 | if ((R->Register[6] & 0x03) == 0x03)\r |
104 | R->Period[3] = 2 * R->Period[2];\r |
105 | }\r |
106 | break;\r |
107 | case 1: /* tone 0 : volume */\r |
108 | case 3: /* tone 1 : volume */\r |
109 | case 5: /* tone 2 : volume */\r |
110 | case 7: /* noise : volume */\r |
111 | R->Volume[c] = R->VolTable[data & 0x0f];\r |
112 | break;\r |
113 | case 6: /* noise : frequency, mode */\r |
114 | n = data;\r |
115 | R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;\r |
116 | n &= 3;\r |
117 | /* N/512,N/1024,N/2048,Tone #3 output */\r |
118 | R->Period[3] = (n == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5 + n));\r |
119 | \r |
120 | /* reset noise shifter */\r |
121 | R->RNG = NG_PRESET;\r |
122 | R->Output[3] = R->RNG & 1;\r |
123 | break;\r |
cc68a136 |
124 | }\r |
125 | }\r |
126 | \r |
127 | /*\r |
128 | WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }\r |
129 | WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }\r |
130 | WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }\r |
131 | WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }\r |
132 | WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }\r |
133 | */\r |
134 | \r |
135 | //static\r |
4f265db7 |
136 | void SN76496Update(short *buffer, int length, int stereo)\r |
cc68a136 |
137 | {\r |
138 | int i;\r |
139 | struct SN76496 *R = &ono_sn;\r |
140 | \r |
141 | /* If the volume is 0, increase the counter */\r |
142 | for (i = 0;i < 4;i++)\r |
143 | {\r |
144 | if (R->Volume[i] == 0)\r |
145 | {\r |
146 | /* note that I do count += length, NOT count = length + 1. You might think */\r |
147 | /* it's the same since the volume is 0, but doing the latter could cause */\r |
148 | /* interferencies when the program is rapidly modulating the volume. */\r |
149 | if (R->Count[i] <= length*STEP) R->Count[i] += length*STEP;\r |
150 | }\r |
151 | }\r |
152 | \r |
153 | while (length > 0)\r |
154 | {\r |
155 | int vol[4];\r |
156 | unsigned int out;\r |
157 | int left;\r |
158 | \r |
159 | \r |
160 | /* vol[] keeps track of how long each square wave stays */\r |
161 | /* in the 1 position during the sample period. */\r |
162 | vol[0] = vol[1] = vol[2] = vol[3] = 0;\r |
163 | \r |
164 | for (i = 0;i < 3;i++)\r |
165 | {\r |
166 | if (R->Output[i]) vol[i] += R->Count[i];\r |
167 | R->Count[i] -= STEP;\r |
168 | /* Period[i] is the half period of the square wave. Here, in each */\r |
169 | /* loop I add Period[i] twice, so that at the end of the loop the */\r |
170 | /* square wave is in the same status (0 or 1) it was at the start. */\r |
171 | /* vol[i] is also incremented by Period[i], since the wave has been 1 */\r |
172 | /* exactly half of the time, regardless of the initial position. */\r |
173 | /* If we exit the loop in the middle, Output[i] has to be inverted */\r |
174 | /* and vol[i] incremented only if the exit status of the square */\r |
175 | /* wave is 1. */\r |
176 | while (R->Count[i] <= 0)\r |
177 | {\r |
178 | R->Count[i] += R->Period[i];\r |
179 | if (R->Count[i] > 0)\r |
180 | {\r |
181 | R->Output[i] ^= 1;\r |
182 | if (R->Output[i]) vol[i] += R->Period[i];\r |
183 | break;\r |
184 | }\r |
185 | R->Count[i] += R->Period[i];\r |
186 | vol[i] += R->Period[i];\r |
187 | }\r |
188 | if (R->Output[i]) vol[i] -= R->Count[i];\r |
189 | }\r |
190 | \r |
191 | left = STEP;\r |
192 | do\r |
193 | {\r |
194 | int nextevent;\r |
195 | \r |
196 | if (R->Count[3] < left) nextevent = R->Count[3];\r |
197 | else nextevent = left;\r |
198 | \r |
199 | if (R->Output[3]) vol[3] += R->Count[3];\r |
200 | R->Count[3] -= nextevent;\r |
201 | if (R->Count[3] <= 0)\r |
202 | {\r |
203 | if (R->RNG & 1) R->RNG ^= R->NoiseFB;\r |
204 | R->RNG >>= 1;\r |
205 | R->Output[3] = R->RNG & 1;\r |
206 | R->Count[3] += R->Period[3];\r |
207 | if (R->Output[3]) vol[3] += R->Period[3];\r |
208 | }\r |
209 | if (R->Output[3]) vol[3] -= R->Count[3];\r |
210 | \r |
211 | left -= nextevent;\r |
212 | } while (left > 0);\r |
213 | \r |
214 | out = vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +\r |
215 | vol[2] * R->Volume[2] + vol[3] * R->Volume[3];\r |
216 | \r |
217 | if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;\r |
218 | \r |
4f265db7 |
219 | if ((out /= STEP)) // will be optimized to shift; max 0x47ff = 18431\r |
cc68a136 |
220 | *buffer += out;\r |
4f265db7 |
221 | if(stereo) buffer+=2; // only left for stereo, to be mixed to right later\r |
222 | else buffer++;\r |
cc68a136 |
223 | \r |
224 | length--;\r |
225 | }\r |
226 | }\r |
227 | \r |
228 | \r |
229 | static void SN76496_set_clock(struct SN76496 *R,int clock)\r |
230 | {\r |
231 | \r |
232 | /* the base clock for the tone generators is the chip clock divided by 16; */\r |
233 | /* for the noise generator, it is clock / 256. */\r |
234 | /* Here we calculate the number of steps which happen during one sample */\r |
235 | /* at the given sample rate. No. of events = sample rate / (clock/16). */\r |
236 | /* STEP is a multiplier used to turn the fraction into a fixed point */\r |
237 | /* number. */\r |
238 | R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;\r |
239 | }\r |
240 | \r |
241 | \r |
242 | static void SN76496_set_gain(struct SN76496 *R,int gain)\r |
243 | {\r |
244 | int i;\r |
245 | double out;\r |
246 | \r |
247 | \r |
248 | gain &= 0xff;\r |
249 | \r |
250 | /* increase max output basing on gain (0.2 dB per step) */\r |
251 | out = MAX_OUTPUT / 3;\r |
252 | while (gain-- > 0)\r |
253 | out *= 1.023292992; /* = (10 ^ (0.2/20)) */\r |
254 | \r |
255 | /* build volume table (2dB per step) */\r |
256 | for (i = 0;i < 15;i++)\r |
257 | {\r |
258 | /* limit volume to avoid clipping */\r |
259 | if (out > MAX_OUTPUT / 3) R->VolTable[i] = MAX_OUTPUT / 3;\r |
260 | else R->VolTable[i] = out;\r |
261 | \r |
262 | out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */\r |
263 | }\r |
264 | R->VolTable[15] = 0;\r |
265 | }\r |
266 | \r |
267 | \r |
268 | //static\r |
269 | int SN76496_init(int clock,int sample_rate)\r |
270 | {\r |
271 | struct SN76496 *R = &ono_sn;\r |
272 | int i;\r |
273 | \r |
274 | //R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);\r |
275 | sn76496_regs = R->Register;\r |
276 | \r |
277 | R->SampleRate = sample_rate;\r |
278 | SN76496_set_clock(R,clock);\r |
279 | \r |
280 | for (i = 0;i < 4;i++) R->Volume[i] = 0;\r |
281 | \r |
282 | R->LastRegister = 0;\r |
283 | for (i = 0;i < 8;i+=2)\r |
284 | {\r |
285 | R->Register[i] = 0;\r |
286 | R->Register[i + 1] = 0x0f; /* volume = 0 */\r |
287 | }\r |
288 | \r |
289 | for (i = 0;i < 4;i++)\r |
290 | {\r |
291 | R->Output[i] = 0;\r |
292 | R->Period[i] = R->Count[i] = R->UpdateStep;\r |
293 | }\r |
294 | R->RNG = NG_PRESET;\r |
295 | R->Output[3] = R->RNG & 1;\r |
296 | \r |
297 | // added\r |
298 | SN76496_set_gain(R, 0);\r |
299 | \r |
300 | return 0;\r |
301 | }\r |
302 | \r |