M17_Implementations

Various implementations

Woj's implementation (/SP5WWP)

Overview

Written in C, it has all the components described by the protocol's specification of the stream and packet modes:

• convolutional encoder with soft Viterbi decoder (utilizing fixed point arithmetic),
• Golay encoder with soft decoder (fixed point),
• bit interleaver and randomizer,
• cyclic redundancy check (CRC) calculation (both LSF and arbitrary input),
• callsign encoder and decoder

There's no support for any encryption yet.

Cloning

Be sure to clone with --recursive to pull the linked libm17 repository, otherwise, building will fail.

git clone https://github.com/M17-Project/M17_Implementations.git --recursive

Building

First, build the shared object libm17.so:

cd M17_Implementations/libm17
make
make install
sudo ldconfig

Then, cd back up to the directory of interest and make again.

Capabilities

Four executables are available:

• m17-coder-sym is used to convert a raw binary data bitstream to symbols. Symbol stream has to be filtered with an appropriate filter before transmission, see the specification document for details.
• m17-decoder-sym decodes a stream of floats at stdin, one sample per symbol. After a valid syncword is detected, decoding process starts. The program expects a stream of synchronized symbols at the input. See the /grc/symbol_recovery.grc file for details.
• m17-packet-encode is a handy tool for generating baseband (or a symbol stream, if needed) for M17 packets. The program expects a limited stream of raw data at the stdin. The number of bytes is set with the -n parameter, range 1 to 800.
• m17-packet-decode decodes incoming packets.

Testing

Stream mode

Both the encoder and the decoder can be tested simultaneously. The test setup should look as follows:
GRC flowgraph -> /tmp/fifo1 -> m17-coder-sym -> /tmp/fifo2 -> m17-decoder-sym -> stdout
To perform a simple test, GNURadio 3.10 is required.

Run the following commands:

mkfifo /tmp/fifo1
mkfifo /tmp/fifo2

This should create 2 named pipes: fifo1 and fifo2. The first one is used for the "transmitted" raw bitstream from GNURadio. The other one is used for the "receiver" part - the symbol stream.

Start gnuradio-companion, open the .grc file included in this repo (/grc/m17_streamer.grc).

Open up 2 terminals and run:
Terminal 1:

cat /tmp/fifo1 | ./m17-coder-sym > /tmp/fifo2

Terminal 2:

cat /tmp/fifo2 | ./m17-decoder-sym

Hit the Execute the flow graph button in GNURadio and watch it roll.

Terminal 2 should show similar results, with the Frame Number advancing each frame:

Packet mode

Packet encoding is available with m17-packet-encoder. Its input parameters are shown below.

-S - source callsign (uppercase alphanumeric string) max. 9 characters
-D - destination callsign (uppercase alphanumeric string) or ALL for broadcast
-C - Channel Access Number (0..15, default - 0)
-n - number of bytes (1 to 798)
-o - output file path/name
-x - binary output (M17 baseband as a packed bitstream)
-r - raw audio output - default (single channel, signed 16-bit LE, +7168 for the +1.0 symbol, 10 samples per symbol)
-s - signed 16-bit LE symbols output
-f - float symbols output compatible with m17-packet-decode
-d - raw audio output - same as -r, but no RRC filtering (debug)
-w - libsndfile wav audio output - default (single channel, signed 16-bit LE, +7168 for the +1.0 symbol, 10 samples per symbol)

Input data is passed over stdin. Example command:

echo -en "\x05Testing M17 packet mode.\x00" | ./m17-packet-encode -S N0CALL -D ALL -C 0 -n 26 -f -o baseband.sym

-en parameter for echo suppresses the trailing newline character and enables the use of \ within the message. \x05 sets the packet data content and stands for text message (as per M17 Specification document, chapter 3.2 - Packet Application).

Output:

DST: ALL	FFFFFFFFFFFF
SRC: N0CALL	00004B13D106
Data CRC:	BFEC
LSF  CRC:	432A
FN:00 (full frame)
0554657374696E67204D3137207061636B6574206D6F64652E00
FN:-- (ending frame)
00BFEC0000000000000000000000000000000000000000000084
FULL: 0554657374696E67204D3137207061636B6574206D6F64652E00BFEC
 SMS: Testing M17 packet mode.

Decode packet created with above sample:

cat baseband.sym | ./m17-packet-decode

Output:

DST: FFFFFFFFFFFF SRC: 00004B13D106 TYPE: 0002 META: 0000000000000000000000000000 LSF_CRC_OK 
Testing M17 packet mode.

Encode directly as wav format (skip sox):

echo -en "\x05Testing M17 packet mode.\x00" | ./m17-packet-encode -S N0CALL -D AB1CDE -C 7 -n 26 -w -o baseband.wav

Output:

DST: AB1CDE	00001F245D51
SRC: N0CALL	00004B13D106
Data CRC:	BFEC
LSF  CRC:	F754
FN:00 (full frame)
0554657374696E67204D3137207061636B6574206D6F64652E00
FN:-- (ending frame)
00BFEC0000000000000000000000000000000000000000000084
FULL: 0554657374696E67204D3137207061636B6574206D6F64652E00BFEC
 SMS: Testing M17 packet mode.

Decode with M17-FME:

m17-fme -r -w baseband.wav -v 1

Output:

M17 Project - Florida Man Edition                          
Build Version: 2024-1-g4f2c15c 
Session Number: A4F5 
M17 Project RF Audio Frame Demodulator. 
SNDFile (.wav, .rrc) Input File: baseband.wav 
Payload Verbosity: 1; 


M17 LSF Frame Sync (08:57:09): 
 DST: AB1CDE    SRC: N0CALL    CAN: 7; Data Packet
 LSF: 00 00 1F 24 5D 51 00 00 4B 13 D1 06 03 82 00
      00 00 00 00 00 00 00 00 00 00 00 00 00 F7 54
      (CRC CHK) E: F754; C: F754;
M17 PKT Frame Sync (08:57:09):  CNT: 00; PBC: 00; EOT: 0;
 pkt: 0554657374696E67204D3137207061636B6574206D6F64652E00
M17 PKT Frame Sync (08:57:09):  CNT: 01; LST: 01; EOT: 1;
 pkt: 00BFEC0000000000000000000000000000000000000000000084 Protocol: SMS;
 SMS: Testing M17 packet mode.
 PKT: 05 54 65 73 74 69 6E 67 20 4D 31 37 20 70 61 63 6B 65 74 20 6D 6F 64 65 2E
      00 BF EC 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
      (CRC CHK) E: BFEC; C: BFEC;
M17  No Frame Sync (08:57:09):