libgdl90

A lightweight GDL90 library that aims to stay easy to use yet portable.

Features

• C99
• No third party dependency
• No dynamic memory allocation
• Unit tests (though currently only for some of the message types)
• Cmake and modular project hierarchy for convenience
• Consists of a single source + header
• Examples, to get you going
• String output of all message types

Purpose

The lib implements the GDL90 display role. Albeit it can process all of the message types mentioned in the official doc, including those meant to be sent by displays, it does not decode anything that isn't strictly part of the protocol (eg. Uplink Data payloads).

Compilation

• Create the build files using cmake (or your IDE)
• Build the project (eg. make or your IDE)
• The following targets will be created :
  • libgdl90.a
  • gdl90-cli
  • gdl90-tests

Use

The easiest way to see how to use it is taking a peek inside the gdl90-cli project contained within this project.

• Add the gdl90.c and gdl90.h files to your project
• Create a GDL90StreamConfig instance on the stack/heap and initialize it with the callbacks, calling GDL90StreamConfig_init(...)
• Create a GDL90Stream instance on the stack/heap and initialize it with the config you created earlier
• For each GDL90 packet (containing one or more messages) call GDL90Stream_process(&gdl90Stream, packet, packetLength)
• You get the GDL90 message instances in the callback you set up earlier (note: if you need to own them, copy them)
• The 0x7e GDL90 flag bytes and CRC are intentionally only checked in GDL90Stream, so if you have a custom protocol you can use GDL90Message directly (note: gdl90-cli uses GDL90Stream, so non-conformant packets won't work with it)

Example projects

gdl90-cli

A simple command line decoder of hex string encoded GDL90 data to show the use of the lib in a C/C++/etc project.

Use :

echo "7e......7e" | gdl90-cli

If you have GDL90 data flowing either through a network interface or stored in a libpcap packet capture, you can use captail to process it, eg.:

tcpdump -X -v -r gdl90.pcap | captail.pl | cut -c 57- | gdl90-cli

gdl90-wasm

A simple - and only partially implemented - decoder to show the use of the lib in a wasm environment. It intentionally avoids the use of emscripten to highlight the portability aspect of the lib, but that's by no means to discourage the use of it.

As I don't actually use wasm, I've only ever tested this example through the most unlikely implementation - a web project. Guess you'll tell me if you try it in a more useful environment.

Use :

• Create the build files using emcmake cmake
• Build the project with make
• Copy the gdl90.wasm, /assets/gdl90.js and /assets/index.html in a directory
• Serve the files using a web server, eg. python3 -m http.server
• After connecting it should display the two test GDL90 messages through console.log

License

The library and all of its components use the MIT license.