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comparison intercom/gsm/gsm.c @ 2:13be24d74cd2

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import intercom-0.4.1
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 09:57:52 +0200
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1:9cadc470e3da 2:13be24d74cd2
1
2 /*
3 RFC3551:
4
5 name of sampling default
6 encoding sample/frame bits/sample rate ms/frame ms/packet
7 __________________________________________________________________
8 GSM frame N/A 8,000 20 20
9
10
11 field field name bits field field name bits
12 ________________________________________________
13 1 LARc[0] 6 39 xmc[22] 3
14 2 LARc[1] 6 40 xmc[23] 3
15 3 LARc[2] 5 41 xmc[24] 3
16 4 LARc[3] 5 42 xmc[25] 3
17 5 LARc[4] 4 43 Nc[2] 7
18 6 LARc[5] 4 44 bc[2] 2
19 7 LARc[6] 3 45 Mc[2] 2
20 8 LARc[7] 3 46 xmaxc[2] 6
21 9 Nc[0] 7 47 xmc[26] 3
22 10 bc[0] 2 48 xmc[27] 3
23 11 Mc[0] 2 49 xmc[28] 3
24 12 xmaxc[0] 6 50 xmc[29] 3
25 13 xmc[0] 3 51 xmc[30] 3
26 14 xmc[1] 3 52 xmc[31] 3
27 15 xmc[2] 3 53 xmc[32] 3
28 16 xmc[3] 3 54 xmc[33] 3
29 17 xmc[4] 3 55 xmc[34] 3
30 18 xmc[5] 3 56 xmc[35] 3
31 19 xmc[6] 3 57 xmc[36] 3
32 20 xmc[7] 3 58 xmc[37] 3
33 21 xmc[8] 3 59 xmc[38] 3
34 22 xmc[9] 3 60 Nc[3] 7
35 23 xmc[10] 3 61 bc[3] 2
36 24 xmc[11] 3 62 Mc[3] 2
37 25 xmc[12] 3 63 xmaxc[3] 6
38 26 Nc[1] 7 64 xmc[39] 3
39 27 bc[1] 2 65 xmc[40] 3
40 28 Mc[1] 2 66 xmc[41] 3
41 29 xmaxc[1] 6 67 xmc[42] 3
42 30 xmc[13] 3 68 xmc[43] 3
43 31 xmc[14] 3 69 xmc[44] 3
44 32 xmc[15] 3 70 xmc[45] 3
45 33 xmc[16] 3 71 xmc[46] 3
46 34 xmc[17] 3 72 xmc[47] 3
47 35 xmc[18] 3 73 xmc[48] 3
48 36 xmc[19] 3 74 xmc[49] 3
49 37 xmc[20] 3 75 xmc[50] 3
50 38 xmc[21] 3 76 xmc[51] 3
51
52 Table 2: Ordering of GSM variables
53
54
55 Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
56 _____________________________________________________________________
57 0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3
58 1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5
59 2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2
60 3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1
61 4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2
62 5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0
63 6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04
64 7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0
65 8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2
66 9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1
67 10 xmc7.2 xmc8.0 xmc8.1 xmc8.2 xmc9.0 xmc9.1 xmc9.2 xmc10.0
68 11 xmc10.1 xmc10.2 xmc11.0 xmc11.1 xmc11.2 xmc12.0 xmc12.1 xcm12.2
69 12 Nc1.0 Nc1.1 Nc1.2 Nc1.3 Nc1.4 Nc1.5 Nc1.6 bc1.0
70 13 bc1.1 Mc1.0 Mc1.1 xmaxc10 xmaxc11 xmaxc12 xmaxc13 xmaxc14
71 14 xmax15 xmc13.0 xmc13.1 xmc13.2 xmc14.0 xmc14.1 xmc14.2 xmc15.0
72 15 xmc15.1 xmc15.2 xmc16.0 xmc16.1 xmc16.2 xmc17.0 xmc17.1 xmc17.2
73 16 xmc18.0 xmc18.1 xmc18.2 xmc19.0 xmc19.1 xmc19.2 xmc20.0 xmc20.1
74 17 xmc20.2 xmc21.0 xmc21.1 xmc21.2 xmc22.0 xmc22.1 xmc22.2 xmc23.0
75 18 xmc23.1 xmc23.2 xmc24.0 xmc24.1 xmc24.2 xmc25.0 xmc25.1 xmc25.2
76 19 Nc2.0 Nc2.1 Nc2.2 Nc2.3 Nc2.4 Nc2.5 Nc2.6 bc2.0
77 20 bc2.1 Mc2.0 Mc2.1 xmaxc20 xmaxc21 xmaxc22 xmaxc23 xmaxc24
78 21 xmaxc25 xmc26.0 xmc26.1 xmc26.2 xmc27.0 xmc27.1 xmc27.2 xmc28.0
79 22 xmc28.1 xmc28.2 xmc29.0 xmc29.1 xmc29.2 xmc30.0 xmc30.1 xmc30.2
80 23 xmc31.0 xmc31.1 xmc31.2 xmc32.0 xmc32.1 xmc32.2 xmc33.0 xmc33.1
81 24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0
82 25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2
83 26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0
84 27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34
85 28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0
86 29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2
87 30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1
88 31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0
89 32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2
90
91 Table 3: GSM payload format
92
93 In the GSM packing used by RTP, the bits SHALL be packed beginning
94 from the most significant bit. Every 160 sample GSM frame is coded
95 into one 33 octet (264 bit) buffer. Every such buffer begins with a
96 4 bit signature (0xD), followed by the MSB encoding of the fields of
97 the frame. The first octet thus contains 1101 in the 4 most
98 significant bits (0-3) and the 4 most significant bits of F1 (0-3) in
99 the 4 least significant bits (4-7).
100
101
102 PT encoding media type clock rate channels
103 name (Hz)
104 ___________________________________________________
105 3 GSM A 8,000 1
106
107 */
108
109 typedef unsigned char Byte;
110
111 static Byte byte;
112 static unsigned mask;
113 static Byte *packed;
114 static int gsmbits[76] = {
115 6, 6, 5, 5, 4, 4, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
116 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3,
117 3, 3, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 2,
118 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3
119 };
120
121 static void pack(short data, int len)
122 {
123 unsigned srcmask;
124
125 for (srcmask = (1 << len-1); srcmask > 0; srcmask /= 2) {
126 if (data & srcmask) {
127 byte += mask;
128 }
129 mask /= 2; // shift right
130 if (0 == mask) {
131 *packed = byte;
132 ++packed;
133 mask = 128;
134 byte = 0;
135 }
136 }
137 }
138
139 int gsmpack(Byte *gsm_frame, short *rpe_frame)
140 {
141 int i;
142
143 byte = 0;
144 mask = 128;
145 packed = gsm_frame;
146
147 pack(0xD, 4); // GSM signature
148 for (i = 0; i < 76; ++i, ++rpe_frame) {
149 pack(*rpe_frame, gsmbits[i]);
150 }
151 *packed = byte;
152
153 return 33;
154 }
155
156 static short unpack(int len)
157 {
158 unsigned srcmask;
159 short data = 0;
160
161 for (srcmask = (1 << len-1); srcmask > 0; srcmask /= 2) {
162 if ((*packed) & mask) {
163 data += srcmask;
164 }
165 mask /= 2; // shift right
166 if (0 == mask) {
167 ++packed;
168 mask = 128;
169 }
170 }
171
172 // fprintf(stderr, "data =%x\n", data);
173 return data;
174 }
175
176 int gsmunpack(short *rpe_frame, Byte *gsm_frame)
177 {
178 int i;
179
180 byte = 0;
181 mask = 128;
182 packed = gsm_frame;
183
184 if (unpack(4) != 0xD) {
185 // fprintf(stderr, "error: gsmunpack\n");
186 return 0; // not GSM signature
187 }
188 for (i = 0; i < 76; ++i, ++rpe_frame) {
189 *rpe_frame = unpack(gsmbits[i]);
190 }
191 // exit(1) ;
192 return 160; // number of PCM samples
193 }
194
195
196

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