packet mode updates

README.md

@@ -27,9 +27,10 @@ syncword is detected, decoding process starts. The program expects a stream of s
 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 798.
+with the `-n` parameter, range 1 to 800.
 
 ### Testing
+#### Stream mode
 Both the encoder and the decoder can be tested simultaneously. The test setup should look as follows:<br>
 `GRC flowgraph -> fifo1 -> m17-coder-sym -> fifo2 -> m17-decoder-sym -> stdout`<br>
 To perform a simple test, GNURadio 3.10 is required.
@@ -46,17 +47,45 @@ Start gnuradio-companion, open the .grc file included in this repo (`/grc/m17_st
 the name of the named pipe to `fifo1` (at the *File Sink* block - the rightmost one). Change the location of it
 if needed.
 
-Open up 2 consoles and run:<br>
-Console 1:
+Open up 2 terminals and run:<br>
+Terminal 1:
 ```
 cat fifo1 | ./m17-coder-sym > fifo2
 ```
-Console 2:
+Terminal 2:
 ```
 cat fifo2 | ./m17-decoder-sym
 ```
 
-Hit the *Execte the flow graph* button in GNURadio and watch it roll.
+Hit the *Execute the flow graph* button in GNURadio and watch it roll.
 
-Console 2 should show similar results, with the Frame Number advancing each frame:
+Terminal 2 should show similar results, with the Frame Number advancing each frame:
 ![image](https://user-images.githubusercontent.com/44336093/209792966-44a7813e-13b3-45d7-92f1-02bb1bdc219f.png)
+
+#### 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 boradcast
+-C - Channel Access Number (0..15, default - 0)
+-n - number of bytes (1 to 800)
+-o - output file path/name
+-x - binary output (M17 baseband as a packed bitstream)
+-r - raw audio output (single channel, signed 16-bit LE, +7168 for the +1.0 symbol, 10 samples per symbol)
+-s - signed 16-bit LE symbols output
+```
+
+Input data is passed over stdin. Example command:
+
+`echo -en "\x05Testing M17 packet mode." | ./m17-packet-encode -S N0CALL -D ALL -C 0 -n 25 -o baseband.rrc`
+
+`-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).
+If a WAVE file format is required for the baseband, sox can be used:
+
+`sox -t raw -r 48000 -b 16 -c 1 -L -e signed-integer baseband.rrc baseband.wav`
+
+This line converts .rrc to .wav. SDRangel successfully decoding a packet:
+![SDRangel screen dump](https://github.com/M17-Project/M17_Implementations/assets/44336093/d2cd195c-6126-4b48-b516-36d20dced9ce)
+
+The two characters at the end of the message are probably CRC bytes erroneously decoded by SDRangel as a part of the text message.