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doc/Binary-file-format: document BFI marker format
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 16 Apr 2023 19:00:46 +0000
parents b4b1c3a192c7
children f469bad44c0e
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820d88b97924 libtest: implement binary file reader
Mychaela Falconia <falcon@freecalypso.org>
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1 We (Themyscira Wireless) define our own binary file format for testing of GSM
820d88b97924 libtest: implement binary file reader
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2 06.10 (FR) and EFR codec functions; this format of ours is an extension of
820d88b97924 libtest: implement binary file reader
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3 classic .gsm format from libgsm/toast. The original libgsm file format is a
820d88b97924 libtest: implement binary file reader
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4 directly abutted sequence of 33-byte libgsm frames, equivalent to RTP frames
820d88b97924 libtest: implement binary file reader
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5 for GSM FR, with the upper nibble of the first byte in each frame equal to 0xD,
820d88b97924 libtest: implement binary file reader
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6 serving as a signature. We simply extend this idea: our version is still a
820d88b97924 libtest: implement binary file reader
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7 directly abutted sequence of binary records, but each record is now one of 3
820d88b97924 libtest: implement binary file reader
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8 possibilities:
820d88b97924 libtest: implement binary file reader
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820d88b97924 libtest: implement binary file reader
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10 - a 33-byte GSM FR frame in libgsm/RTP format, 0xD signature
820d88b97924 libtest: implement binary file reader
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11 - a 31-byte GSM EFR frame in RTP format (ETSI TS 101 318), 0xC signature
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12 - a 2-byte Themyscira-extension BFI marker, 0xBF signature, see below
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820d88b97924 libtest: implement binary file reader
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14 File reading functions begin by reading only one byte; this byte, once decoded,
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15 tells us how many more bytes need to be read, and frame synchronization is thus
820d88b97924 libtest: implement binary file reader
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16 maintained.
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598ee3ce238b doc/Binary-file-format: document .gsmx suffix
Mychaela Falconia <falcon@freecalypso.org>
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18 The recommended filename suffix for extended-libgsm binary files in the present
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19 format is .gsmx; of course dot-separated filename suffixes hold absolutely no
598ee3ce238b doc/Binary-file-format: document .gsmx suffix
Mychaela Falconia <falcon@freecalypso.org>
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20 special meaning on Unix systems, but many developers still strongly prefer to
598ee3ce238b doc/Binary-file-format: document .gsmx suffix
Mychaela Falconia <falcon@freecalypso.org>
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21 have them for psychological comfort.
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b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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23 Any gsmx file (FR or EFR) can be dumped in human-readable form with our
b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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24 gsmrec-dump utility. This utility turns every read frame from bytes into codec
b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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25 parameters with gsm_explode() or EFR_frame2params(), and then displays those
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26 parameters in a sensible manner, with a per-frame header line followed by 4
b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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27 lines of subframe parameters.
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b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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29 FR and EFR frames are not expected to be mixed in the same stream recording;
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30 our low-level binary file reading function and gsmrec-dump will grok such mixing
b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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31 just fine, but each higher-level test program (beyond gsmrec-dump) is expected
b4b1c3a192c7 doc/Binary-file-format: document gsmrec-dump
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32 to be written for only one codec, either FR or EFR.
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34 BFI marker format
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35 =================
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37 Every 20 ms frame in our gsmx files is either a good FR/EFR frame or a BFI (Bad
7e490a8efe8a doc/Binary-file-format: document BFI marker format
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38 Frame Indication) marker. The BFI marker format used in our gsmx file format is
7e490a8efe8a doc/Binary-file-format: document BFI marker format
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39 the same format which we (Themyscira Wireless) previously used in our GSM RAN
7e490a8efe8a doc/Binary-file-format: document BFI marker format
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40 RTP transport, before switching to our current TRAUlike RTP format. This BFI
7e490a8efe8a doc/Binary-file-format: document BFI marker format
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41 marker format is quite simple:
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7e490a8efe8a doc/Binary-file-format: document BFI marker format
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43 byte 0: 0xBF signature;
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44 byte 1: least-significant bit encoding TAF per GSM 06.31 or GSM 06.81,
7e490a8efe8a doc/Binary-file-format: document BFI marker format
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45 section 6.1.1 in both documents; other bits are reserved.