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
  • Rev A information frames
  • APDU headers, civil-time variants, reserved-bit validation, and segmentation metadata
  • stateful product-file reassembly across uplink messages
  • out-of-order and duplicate-segment handling
  • TWGO repeated-header removal for products 8 and 11–17
  • Generic Text APDUs, whole-record packing, and exact six-bit DLAC encode/decode
  • DLAC control codes and code-28 run-length spaces
  • NEXRAD APDUs and block payloads
  • named, lossless raw preservation for product schemas outside Garmin Rev A
• 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
  uplink_reassembly.rs   Segmented FIS-B product-file reassembly
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
cargo run --example uplink_reassembly

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
cargo clippy --all-targets -- -D warnings

Protocol scope and completion

The built-in support matrix has no incomplete entries for behavior defined by the Garmin GDL 90 Public ICD Rev A. The uplink implementation now includes variable APDU headers, one-based segmentation metadata, stateful reassembly, TWGO repeated-header handling, and the full FIS-B DLAC code table.

• I-Frame type handling is strict to Rev A Table 18: 0x0 is FIS-B APDU, 0xF is developmental, and 0x1..=0xE are reserved.
• The historical APDU A/G/P positions are treated as reserved bits in the operational UAT/FIS-B profile and must be zero.
• Generic Text Type 2 and NEXRAD Global Block Representation payloads—the product schemas contained in Rev A—are decoded and encoded.
• Other FAA/FIS-B registry product IDs are named where known and preserve their exact APDU header and payload bytes. Schemas not contained in Rev A are intentionally not guessed.
• ApduReassembler is stateful by design. Applications decide when to discard incomplete product files according to their own receive-window or timeout policy.

Inspect the built-in support matrix with:

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

License

MIT, see LICENSE.