gdl90

Rust library and CLI for encoding, decoding, transporting, recording, and analyzing GDL90 traffic, including ForeFlight extension messages, Garmin control-panel ASCII messages, and documented UAT uplink payloads.

What the crate currently includes

• HDLC-style GDL90 framing
  • byte stuffing and unstuffing
  • CRC-CCITT/FCS generation and validation
  • frame and stream decoders
• Standard GDL90 message support
  • Heartbeat
  • Initialization
  • Uplink Data
  • Ownship Report
  • Traffic Report
  • Basic Report
  • Long Report
  • Height Above Terrain
  • Ownship Geometric Altitude
  • pass-through ADS-B inner field decoding for basic and long reports
• ForeFlight support
  • ID message (0x65/0x00)
  • AHRS message (0x65/0x01)
  • discovery announcement parsing
  • UDP send/receive helpers using ForeFlight's documented ports
  • ForeFlight-compatible multi-message UDP datagram encoding
• Garmin control-panel ASCII message support
  • Call Sign
  • Mode
  • VFR Code
• UAT uplink parsing and encoding for the documented structures
  • information frames
  • APDU headers, optional time metadata, and segmentation metadata
  • Generic Text APDUs, record packing, and DLAC encode/decode
  • NEXRAD APDUs and block payloads
  • named-but-raw preservation for additional FIS-B product IDs
• Session tooling
  • read, write, and append recorded UDP datagram files
  • decode, validate, report, capture, and replay session traffic
• Analysis and reporting
  • per-session summaries
  • datagram validation with issue reporting
  • detailed text and JSON reports
• Support/status helpers
  • Garmin ICD section coverage matrix
  • RS-422 bus profile and connector mapping
  • control-panel serial profiles and connector mapping
• Bandwidth scheduling helpers
  • byte-budget calculation
  • message prioritization across heartbeat, ownship, traffic, and uplinks

Project layout

src/
  lib.rs          Public exports
  frame.rs        Framing, escaping, CRC/FCS, and stream decoding
  message.rs      Standard GDL90 messages and pass-through ADS-B payloads
  foreflight.rs   ForeFlight extension messages and datagram encoding
  control.rs      Garmin control-panel ASCII messages
  uplink.rs       UAT uplink payloads, APDUs, DLAC text, and NEXRAD blocks
  transport.rs    UDP send/receive helpers and ForeFlight discovery helpers
  session.rs      Recorded datagram parsing, writing, and replay helpers
  analysis.rs     Session summary and validation helpers
  report.rs       Detailed text and JSON reporting
  support.rs      ICD support matrix and interface profiles
  bandwidth.rs    Bandwidth-budget scheduling helpers
  util.rs         Internal shared codecs and helpers
  error.rs        Shared error type
  bin/gdl90.rs    CLI utility
examples/
  end_to_end.rs   Standard message framing round trip
  foreflight.rs   ForeFlight ID and AHRS examples
tests/
  protocol.rs     Protocol encode/decode coverage
  session.rs      Session file coverage
  analysis.rs     Analysis and validation coverage
  report.rs       Text and JSON report coverage

Quick start

use gdl90::{Heartbeat, HeartbeatStatus, Message};
use gdl90::frame::decode_frame;

let heartbeat = Message::Heartbeat(Heartbeat {
    status: HeartbeatStatus {
        gps_position_valid: true,
        maintenance_required: false,
        ident: false,
        address_type_talkback: false,
        gps_battery_low: false,
        ratcs: false,
        uat_initialized: true,
        csa_requested: false,
        csa_not_available: false,
        utc_ok: true,
    },
    timestamp_seconds_since_midnight: 123,
    uplink_count: 2,
    basic_and_long_count: 17,
});

let frame = heartbeat.encode_frame().unwrap();
let clear = decode_frame(&frame).unwrap();
let decoded = Message::decode(&clear).unwrap();

assert_eq!(decoded, heartbeat);

The library is split into focused modules:

• gdl90::frame for raw framing and stream decoding
• gdl90::message for standard GDL90 messages
• gdl90::foreflight for ForeFlight extensions
• gdl90::control for Garmin control-panel ASCII messages
• gdl90::uplink for UAT uplink and APDU parsing
• gdl90::transport for UDP discovery, send, and receive helpers
• gdl90::session, analysis, and report for recorded datagram workflows
• gdl90::support and bandwidth for implementation status and scheduling helpers

Examples

cargo run --example end_to_end
cargo run --example foreflight

CLI

Run the built-in CLI with:

cargo run --bin gdl90 -- --help

Current commands:

decode-frame <hex-frame>
decode-stream <hex-stream>
decode-file <session-file>
report-file <session-file>
report-file-json <session-file> [output-file]
support-status [--missing]
interface-profiles
analyze-file <session-file>
validate-file <session-file>
listen [bind-addr]
discover [bind-addr] [timeout-seconds]
capture [bind-addr] <output-file> [count]
send-demo <target-host:port> [count] [interval-ms]
replay-file <session-file> <target-host:port> [default-interval-ms]

Examples:

cargo run --bin gdl90 -- decode-frame 7E008141DBD00802B38B7E
cargo run --bin gdl90 -- decode-stream 7E008141DBD00802B38B7E7E0B00C88008787E
cargo run --bin gdl90 -- decode-file tests/data/demo_session.txt
cargo run --bin gdl90 -- report-file tests/data/demo_session.txt
cargo run --bin gdl90 -- report-file-json tests/data/demo_session.txt report.json
cargo run --bin gdl90 -- analyze-file tests/data/demo_session.txt
cargo run --bin gdl90 -- validate-file tests/data/demo_session.txt
cargo run --bin gdl90 -- support-status --missing
cargo run --bin gdl90 -- interface-profiles

Defaults for network-oriented commands:

• ForeFlight discovery bind port: 63093
• GDL90 traffic bind port: 4000
• capture keeps running until interrupted when count is omitted or 0
• report-file-json prints JSON to stdout when output-file is omitted

Session file format

Session files are plain text with one UDP datagram per line:

# comment
7E008141DBD00802B38B7E
@250 7E008141DBD00802B38B7E

• blank lines and lines starting with # are ignored
• spaces, : and - are accepted inside hex payloads
• @<ms> <hex> adds an optional replay delay before that datagram
• each line stores a full UDP datagram, which may contain one or more framed GDL90 messages

Validation

Verified in this repository with:

cargo fmt --check
cargo test

Current limits

Most of the Garmin ICD surface implemented in this repository is marked complete by the built-in support matrix. The remaining gaps are concentrated in uplink product internals that depend on material outside this repository.

• APDU product-descriptor option fields are still externally specified and are not fully modeled
• full linked or segmented FIS-B product reassembly is not implemented
• Generic Text support covers the implemented mappings and the verified Appendix K pipe-character correction, but exact full Appendix K behavior is not guaranteed
• Generic Text and NEXRAD products are payload-decoded; other FAA/SBS registry products are identified and preserved raw rather than fully decoded
• future or ancillary UAT/FIS-B products still depend on external RTCA or FAA definitions

Inspect the built-in support matrix with:

cargo run --bin gdl90 -- support-status
cargo run --bin gdl90 -- support-status --missing

License

MIT, see LICENSE.