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view intercom/gsm/gsm.c @ 2:13be24d74cd2
import intercom-0.4.1
| author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
|---|---|
| date | Fri, 25 Jun 2010 09:57:52 +0200 |
| parents | |
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/* RFC3551: name of sampling default encoding sample/frame bits/sample rate ms/frame ms/packet __________________________________________________________________ GSM frame N/A 8,000 20 20 field field name bits field field name bits ________________________________________________ 1 LARc[0] 6 39 xmc[22] 3 2 LARc[1] 6 40 xmc[23] 3 3 LARc[2] 5 41 xmc[24] 3 4 LARc[3] 5 42 xmc[25] 3 5 LARc[4] 4 43 Nc[2] 7 6 LARc[5] 4 44 bc[2] 2 7 LARc[6] 3 45 Mc[2] 2 8 LARc[7] 3 46 xmaxc[2] 6 9 Nc[0] 7 47 xmc[26] 3 10 bc[0] 2 48 xmc[27] 3 11 Mc[0] 2 49 xmc[28] 3 12 xmaxc[0] 6 50 xmc[29] 3 13 xmc[0] 3 51 xmc[30] 3 14 xmc[1] 3 52 xmc[31] 3 15 xmc[2] 3 53 xmc[32] 3 16 xmc[3] 3 54 xmc[33] 3 17 xmc[4] 3 55 xmc[34] 3 18 xmc[5] 3 56 xmc[35] 3 19 xmc[6] 3 57 xmc[36] 3 20 xmc[7] 3 58 xmc[37] 3 21 xmc[8] 3 59 xmc[38] 3 22 xmc[9] 3 60 Nc[3] 7 23 xmc[10] 3 61 bc[3] 2 24 xmc[11] 3 62 Mc[3] 2 25 xmc[12] 3 63 xmaxc[3] 6 26 Nc[1] 7 64 xmc[39] 3 27 bc[1] 2 65 xmc[40] 3 28 Mc[1] 2 66 xmc[41] 3 29 xmaxc[1] 6 67 xmc[42] 3 30 xmc[13] 3 68 xmc[43] 3 31 xmc[14] 3 69 xmc[44] 3 32 xmc[15] 3 70 xmc[45] 3 33 xmc[16] 3 71 xmc[46] 3 34 xmc[17] 3 72 xmc[47] 3 35 xmc[18] 3 73 xmc[48] 3 36 xmc[19] 3 74 xmc[49] 3 37 xmc[20] 3 75 xmc[50] 3 38 xmc[21] 3 76 xmc[51] 3 Table 2: Ordering of GSM variables Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 _____________________________________________________________________ 0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3 1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5 2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2 3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1 4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2 5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0 6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04 7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0 8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2 9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1 10 xmc7.2 xmc8.0 xmc8.1 xmc8.2 xmc9.0 xmc9.1 xmc9.2 xmc10.0 11 xmc10.1 xmc10.2 xmc11.0 xmc11.1 xmc11.2 xmc12.0 xmc12.1 xcm12.2 12 Nc1.0 Nc1.1 Nc1.2 Nc1.3 Nc1.4 Nc1.5 Nc1.6 bc1.0 13 bc1.1 Mc1.0 Mc1.1 xmaxc10 xmaxc11 xmaxc12 xmaxc13 xmaxc14 14 xmax15 xmc13.0 xmc13.1 xmc13.2 xmc14.0 xmc14.1 xmc14.2 xmc15.0 15 xmc15.1 xmc15.2 xmc16.0 xmc16.1 xmc16.2 xmc17.0 xmc17.1 xmc17.2 16 xmc18.0 xmc18.1 xmc18.2 xmc19.0 xmc19.1 xmc19.2 xmc20.0 xmc20.1 17 xmc20.2 xmc21.0 xmc21.1 xmc21.2 xmc22.0 xmc22.1 xmc22.2 xmc23.0 18 xmc23.1 xmc23.2 xmc24.0 xmc24.1 xmc24.2 xmc25.0 xmc25.1 xmc25.2 19 Nc2.0 Nc2.1 Nc2.2 Nc2.3 Nc2.4 Nc2.5 Nc2.6 bc2.0 20 bc2.1 Mc2.0 Mc2.1 xmaxc20 xmaxc21 xmaxc22 xmaxc23 xmaxc24 21 xmaxc25 xmc26.0 xmc26.1 xmc26.2 xmc27.0 xmc27.1 xmc27.2 xmc28.0 22 xmc28.1 xmc28.2 xmc29.0 xmc29.1 xmc29.2 xmc30.0 xmc30.1 xmc30.2 23 xmc31.0 xmc31.1 xmc31.2 xmc32.0 xmc32.1 xmc32.2 xmc33.0 xmc33.1 24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0 25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2 26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0 27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34 28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0 29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2 30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1 31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0 32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2 Table 3: GSM payload format In the GSM packing used by RTP, the bits SHALL be packed beginning from the most significant bit. Every 160 sample GSM frame is coded into one 33 octet (264 bit) buffer. Every such buffer begins with a 4 bit signature (0xD), followed by the MSB encoding of the fields of the frame. The first octet thus contains 1101 in the 4 most significant bits (0-3) and the 4 most significant bits of F1 (0-3) in the 4 least significant bits (4-7). PT encoding media type clock rate channels name (Hz) ___________________________________________________ 3 GSM A 8,000 1 */ typedef unsigned char Byte; static Byte byte; static unsigned mask; static Byte *packed; static int gsmbits[76] = { 6, 6, 5, 5, 4, 4, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 2, 2, 6, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3 }; static void pack(short data, int len) { unsigned srcmask; for (srcmask = (1 << len-1); srcmask > 0; srcmask /= 2) { if (data & srcmask) { byte += mask; } mask /= 2; // shift right if (0 == mask) { *packed = byte; ++packed; mask = 128; byte = 0; } } } int gsmpack(Byte *gsm_frame, short *rpe_frame) { int i; byte = 0; mask = 128; packed = gsm_frame; pack(0xD, 4); // GSM signature for (i = 0; i < 76; ++i, ++rpe_frame) { pack(*rpe_frame, gsmbits[i]); } *packed = byte; return 33; } static short unpack(int len) { unsigned srcmask; short data = 0; for (srcmask = (1 << len-1); srcmask > 0; srcmask /= 2) { if ((*packed) & mask) { data += srcmask; } mask /= 2; // shift right if (0 == mask) { ++packed; mask = 128; } } // fprintf(stderr, "data =%x\n", data); return data; } int gsmunpack(short *rpe_frame, Byte *gsm_frame) { int i; byte = 0; mask = 128; packed = gsm_frame; if (unpack(4) != 0xD) { // fprintf(stderr, "error: gsmunpack\n"); return 0; // not GSM signature } for (i = 0; i < 76; ++i, ++rpe_frame) { *rpe_frame = unpack(gsmbits[i]); } // exit(1) ; return 160; // number of PCM samples }