gengo-mbus

M-Bus / Meter-Bus (EN 13757) frame and telegram decoder for Gengo.

gengo-mbus accepts raw M-Bus frames as hex strings and returns structured decode results. It is transport-agnostic: serial, TCP, radio gateway, and file input are all outside the decoder itself.

The implementation is currently a single Gengo module in mbus.gengo, with a small CLI and a test corpus.

Status

Current capabilities:

• frame decoding for ACK, short, control, and long frames
• checksum and CRC-16 validation
• variable data telegram decoding
• fixed data telegram decoding
• compact data and format data identification with partial body export
• JSON and flat-map export helpers
• CLI for decoding a single hex payload from stdin

Current limitations:

• compact data telegrams are identified, but not expanded without a matching format template
• format data telegrams expose descriptor parsing, not full compact-template application
• encrypted / manufacturer-specific payload handling is limited

Quick Start

Decode a frame from a Gengo script:

mbus := import("./mbus")
std := import("std")

hex_str := "683D3D68080B7221000000B05C021B120000000C784904006402750A0001FD711E2F2F0A6620020AFB1A310502FD971D00002F2F2F2F2F2F2F2F2F2F2F2F2F2F2FDD16"

result := mbus.decode(hex_str)
std.io.println("ok:", result.ok)

if result.telegram != null {
    std.io.println(mbus.telegram_to_json(result.telegram))
}

Run the CLI:

echo "683D3D68080B7221000000B05C021B120000000C784904006402750A0001FD711E2F2F0A6620020AFB1A310502FD971D00002F2F2F2F2F2F2F2F2F2F2F2F2F2F2FDD16" | ../gengo/zig-out/bin/gengo cli.gengo

Public API

Main entrypoints in mbus.gengo:

• decode(hex_str string) DecodeResult
• decode_one(hex_str string) ?Telegram
• decode_frame(hex_str string) Frame
• decode_telegram(frame Frame) Telegram

Export helpers:

• telegram_to_json(t Telegram) string
• frame_to_json(f Frame) string
• decode_result_to_json(r DecodeResult) string
• telegram_to_map(t Telegram) map[string]string

Utilities:

• crc16_en13757(hex_str string) ?int
• decode_status_flags(status_byte int) StatusFlags

Testing

Run all test suites:

./run_tests.sh

run_tests.sh uses GENGO_BIN if set. Otherwise it falls back to a local ../gengo/zig-out/bin/gengo binary when present, then to gengo on PATH.

Important test files:

• test_all.gengo
• test_decode.gengo
• test_fixed_data.gengo
• test_crc16.gengo
• test_edge_cases.gengo
• test_export.gengo
• test_corpus2.gengo

Documentation

• USAGE.md: walkthrough and examples
• ARCHITECTURE.md: internal structure and design notes

Project Layout

gengo-mbus/
  mbus.gengo
  cli.gengo
  test_all.gengo
  test_decode.gengo
  test_fixed_data.gengo
  test_crc16.gengo
  test_edge_cases.gengo
  test_export.gengo
  test_corpus2.gengo
  run_tests.sh
  README.md
  USAGE.md
  ARCHITECTURE.md