kopia lustrzana https://github.com/M17-Project/M17_Implementations
97 wiersze
4.1 KiB
Markdown
97 wiersze
4.1 KiB
Markdown
# M17_Implementations
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Various implementations
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## Woj's implementation (/SP5WWP)
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### Overview
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Written in C, it has all the components described by the protocol's specification of the stream and packet modes:
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- convolutional encoder with soft Viterbi decoder (utilizing fixed point arithmetic),
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- Golay encoder with soft decoder (fixed point),
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- bit interleaver and randomizer,
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- cyclic redundancy check (CRC) calculation (both LSF and arbitrary input),
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- callsign encoder and decoder
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There's no support for **any** encryption yet.
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### Building
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First, build the shared object `libm17.so`:
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```
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cd M17_Implementations/libm17
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make
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make install
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sudo ldconfig
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```
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Then, `cd` back up to the directory of interest and ```make``` again.
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### Capabilities
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Four executables are available:
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- `m17-coder-sym` is used to convert a raw binary data bitstream to symbols. Symbol stream has to be
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filtered with an appropriate filter before transmission, see the specification document for details.
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- `m17-decoder-sym` decodes a stream of floats at `stdin`, one sample per symbol. After a valid
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syncword is detected, decoding process starts. The program expects a stream of synchronized symbols
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at the input. See the `/grc/symbol_recovery.grc` file for details.
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- `m17-packet-encode` is a handy tool for generating baseband (or a symbol stream, if needed) for
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M17 packets. The program expects a limited stream of raw data at the stdin. The number of bytes is set
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with the `-n` parameter, range 1 to 800.
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- `m17-packet-decode` decodes incoming packets.
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### Testing
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#### Stream mode
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Both the encoder and the decoder can be tested simultaneously. The test setup should look as follows:<br>
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`GRC flowgraph -> fifo1 -> m17-coder-sym -> fifo2 -> m17-decoder-sym -> stdout`<br>
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To perform a simple test, GNURadio 3.10 is required.
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Run the following commands:
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```
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mkfifo fifo1
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mkfifo fifo2
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```
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This should create 2 named pipes: `fifo1` and `fifo2`. The first one is used for the "transmitted" raw
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bitstream from GNURadio. The other one is used for the "receiver" part - the symbol stream.
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Start gnuradio-companion, open the .grc file included in this repo (`/grc/m17_streamer.grc`) and change
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the name of the named pipe to `fifo1` (at the *File Sink* block - the rightmost one). Change the location of it
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if needed.
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Open up 2 terminals and run:<br>
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Terminal 1:
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```
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cat fifo1 | ./m17-coder-sym > fifo2
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```
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Terminal 2:
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```
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cat fifo2 | ./m17-decoder-sym
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```
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Hit the *Execute the flow graph* button in GNURadio and watch it roll.
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Terminal 2 should show similar results, with the Frame Number advancing each frame:
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#### Packet mode
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Packet encoding is available with `m17-packet-encoder`. Its input parameters are shown below.
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```
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-S - source callsign (uppercase alphanumeric string) max. 9 characters
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-D - destination callsign (uppercase alphanumeric string) or ALL for broadcast
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-C - Channel Access Number (0..15, default - 0)
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-n - number of bytes (1 to 798)
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-o - output file path/name
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-x - binary output (M17 baseband as a packed bitstream)
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-r - raw audio output - default (single channel, signed 16-bit LE, +7168 for the +1.0 symbol, 10 samples per symbol)
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-s - signed 16-bit LE symbols output
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```
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Input data is passed over stdin. Example command:
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`echo -en "\x05Testing M17 packet mode." | ./m17-packet-encode -S N0CALL -D ALL -C 0 -n 25 -o baseband.rrc`
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`-en` parameter for `echo` suppresses the trailing newline character and enables the use of `\` within the message.
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`\x05` sets the packet data content and stands for text message (as per M17 Specification document, chapter 3.2 - Packet Application).
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If a WAVE file format is required for the baseband, sox can be used:
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`sox -t raw -r 48000 -b 16 -c 1 -L -e signed-integer baseband.rrc baseband.wav`
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This line converts .rrc to .wav. SDRangel successfully decoding a packet:
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The two characters at the end of the message are probably CRC bytes erroneously decoded by SDRangel as a part of the text message.
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