FreeCalypso > hg > gsm-codec-lib
comparison libgsmfr2/tfo_dtxd.c @ 532:5a3535470c95
libgsmfr2 TFO: implement DTXd function
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Thu, 19 Sep 2024 21:00:18 +0000 |
| parents | |
| children |
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| 531:c7b1e796e91b | 532:5a3535470c95 |
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| 1 /* | |
| 2 * The function implemented in this module is a post-processor to be invoked | |
| 3 * after Rx DTX preproc functions if the Rx DTX handler block is used as a | |
| 4 * TFO transform with DTXd enabled. It selectively transforms certain | |
| 5 * preproc output frames (CN and silence frames specifically) into SID, | |
| 6 * thereby allowing the network operator to reap the benefits of DTX on | |
| 7 * the radio downlink leg. | |
| 8 */ | |
| 9 | |
| 10 #include <stdint.h> | |
| 11 #include "tw_gsmfr.h" | |
| 12 #include "pp_state.h" | |
| 13 | |
| 14 int gsmfr_tfo_xfrm_dtxd(struct gsmfr_preproc_state *st, uint8_t *frame) | |
| 15 { | |
| 16 uint8_t *p, sub; | |
| 17 | |
| 18 if (!st->dtxd_sid_flag) | |
| 19 return 1; /* SP=1: output is a speech frame */ | |
| 20 /* turn the output frame into SID */ | |
| 21 p = frame + 5; /* skip magic+LARc */ | |
| 22 for (sub = 0; sub < 4; sub++) { | |
| 23 *p++ = 0; | |
| 24 *p++ &= 0x1F; /* upper 5 bits of Xmaxc field */ | |
| 25 *p++ &= 0x80; /* and the lsb spilling into the next byte */ | |
| 26 *p++ = 0; | |
| 27 *p++ = 0; | |
| 28 *p++ = 0; | |
| 29 *p++ = 0; | |
| 30 } | |
| 31 return 0; /* SP=0: output is SID */ | |
| 32 } |