Various implementations
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
Be sure to clone with --recursive to pull the required linked repositories, otherwise building will fail.
git clone --recursive https://github.com/M17-Project/M17_Implementations.git
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 (SP5WWP/m17-*) and make again.
Four executables are available:
m17-coder-symis 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-symdecodes a stream of floats atstdin, 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.grcfile for details.m17-packet-encodeis 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-nparameter, range 1 to 823.m17-packet-decodedecodes incoming packets.
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:
m17-coder-sym and m17-decoder-sym now offer support for ECDSA (secp256r1 256-bit prime field Weierstrass curve) stream signing and verification, AES (128, 192, 256-bit) and scrambler (8, 16, 24-bit) stream payload encryption. See relevant input parameters below and sample_* text files provided in m17-coder-sym and m17-decoder-sym folders.
The signature occupies 4 last data frames of the stream. It is generated after the data transmission has finished. When there's no more user data to transmit, a hash based on all the contents is calculated. That hash value is then signed with the user's private key.
Stream encoding (m17-decoder-sym) has optional input parameters, shown below.
-s - Private key for ECDSA signature, 32 bytes (-s [hex_string|key_file]),
-K - AES encryption key (-K [hex_string|text_file]),
-k - Scrambler encryption seed value (-k [hex_string]),
-D - Debug mode,
-h - help / print usage
Stream decoding (m17-decoder-sym) has optional input parameters, shown below.
-c - Display decoded callsigns,
-v - Display Viterbi error metrics,
-m - Display META fields,
-l - Display LSF CRC checks,
-d - Set syncword detection threshold (decimal value),
-s - Public key for ECDSA signature, 64 bytes (-s [hex_string|key_file]),
-K - AES encryption key (-K [hex_string|text_file]),
-k - Scrambler encryption seed value (-k [hex_string]),
-h - help / print usage
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)
-T - SMS Text Message (example: -T "Hello World! This is a text message")
-R - Raw Hex Octets (example: -R 010203040506070809)
-n - number of bytes, only when pre-encoded data is passed over stdin (1 to 823)
-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 can be pre-encoded and 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:
SMS: Testing M17 packet mode.
DST: ALL FFFFFFFFFFFF
SRC: N0CALL 00004B13D106
CAN: 00
Data CRC: BFEC
LSF CRC: 432A
FN:00 (full frame)
FN:-- (ending frame)
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
Decode packet created with above sample:
cat baseband.sym | ./m17-packet-decode
Output:
DST: FFFFFFFFFFFF SRC: 00004B13D106 TYPE: 0002 META: 0000000000000000000000000000 LSF_CRC_OK
SMS: Testing M17 packet mode.
Encode User Text String as wav format:
./m17-packet-encode -S N0CALL -D AB1CDE -T "This is an SMS Text Message Generated by m17-packet-encode" -C 7 -w -o baseband.wav
Output:
SMS: This is an SMS Text Message Generated by m17-packet-encode
DST: AB1CDE 00001F245D51
SRC: N0CALL 00004B13D106
CAN: 07
Data CRC: FD81
LSF CRC: F754
FN:00 (full frame)
FN:01 (full frame)
FN:-- (ending frame)
PKT: 05 54 68 69 73 20 69 73 20 61 6E 20 53 4D 53 20 54 65 78 74 20 4D 65 73 73
61 67 65 20 47 65 6E 65 72 61 74 65 64 20 62 79 20 6D 31 37 2D 70 61 63 6B
65 74 2D 65 6E 63 6F 64 65 00 FD 81 00 00 00 00 00 00 00 00 00 00 00 00 00
Decode with M17-FME:
m17-fme -r -w baseband.wav -v 1
Output:
M17 Project - Florida Man Edition
Build Version: 2024-10-g060dd21
Session Number: A751
M17 Project RF Audio Frame Demodulator.
SNDFile (.wav, .rrc) Input File: baseband.wav
Payload Verbosity: 1;
M17 LSF Frame Sync (16:12:34):
DST: AB1CDE SRC: N0CALL CAN: 7; Data Packet FT: 0382; ET: 0; ES: 0;
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 (16:12:34): CNT: 00; PBC: 00; EOT: 0;
pkt: 055468697320697320616E20534D532054657874204D65737300
M17 PKT Frame Sync (16:12:34): CNT: 01; PBC: 01; EOT: 0;
pkt: 6167652047656E657261746564206279206D31372D7061636B04
M17 PKT Frame Sync (16:12:34): CNT: 02; LST: 12; EOT: 1;
pkt: 65742D656E636F646500FD8100000000000000000000000000B0 Protocol: SMS;
SMS: This is an SMS Text Message Generated by m17-packet-encode
PKT: 05 54 68 69 73 20 69 73 20 61 6E 20 53 4D 53 20 54 65 78 74 20 4D 65 73 73
61 67 65 20 47 65 6E 65 72 61 74 65 64 20 62 79 20 6D 31 37 2D 70 61 63 6B
65 74 2D 65 6E 63 6F 64 65 00 FD 81 00 00 00 00 00 00 00 00 00 00 00 00 00
(CRC CHK) E: FD81; C: FD81;
Encode Raw Hex Octet String as float symbol format:
./m17-packet-encode -S N0CALL -D AB1CDE -R 010203040506070809 -C 7 -f -o float.sym
Output:
Raw Len: 9; Raw Octets: 01 02 03 04 05 06 07 08 09
DST: AB1CDE 00001F245D51
SRC: N0CALL 00004B13D106
CAN: 07
Data CRC: D7CE
LSF CRC: F754
FN:-- (ending frame)
PKT: 01 02 03 04 05 06 07 08 09 D7 CE 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Decode (rolling) packets created with above sample:
tail -f float.sym | ./m17-packet-decode
Output:
DST: 00001F245D51 SRC: 00004B13D106 TYPE: 0382 META: 0000000000000000000000000000 LSF_CRC_OK
PKT: 01 02 03 04 05 06 07 08 09 D7 CE