Decode every standard NMEA 2000 PGN, checked against real frames - #30
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NMEA 2000 coverage was thirteen hand-written single-frame PGNs and two fast packets, with 41 names. canboat (Apache 2.0) publishes definitions for nearly every PGN; tools/build_n2k_table.py distils the standard ones into a 133 kB table (216 PGNs, 1,433 fields, 125 lookups) that ships with the package and the binary, with canboat's licence beside it. The hand-written decoders keep precedence. Where both exist, they agree on every shared value across the real marine recording: 800 headings, 400 positions, 400 wind readings, rate of turn, COG and SOG, the GNSS fix after reassembly. Proprietary PGNs, which canboat defines once per manufacturer, are named as proprietary and not decoded; repeating groups (satellites, AIS slots) stop at the group, so one satellite's PRN is never shown as "the" PRN. Validity comes from the table's own ranges, so reserved, error and not-available codes are never readings, signed fields included (0x7FFF is not available; 0xFFFF is -1). Temperatures are converted from kelvin. The reassembler now reassembles all 122 standard fast-packet PGNs, not 13. On the marine log that adds five message types, and 21 of its 29 PGNs decode instead of 11. Found on the way: both decoders rounded every value to six places. That reported a rate of turn of -0.0001047 rad/s as -0.000105 and cut a 1e-7 degree position to ten centimetres. Values now round to their own resolution.
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What
NMEA 2000 coverage was 13 hand-written single-frame PGNs, 2 fast packets and 41 names. canboat (Apache License 2.0) publishes definitions for nearly every PGN.
tools/build_n2k_table.pydistils canboat's standard PGNs intocanlab/core/data/n2k_pgns.json: 216 PGNs, 1,433 fields, 125 lookups, 133 kB.CANBOAT-NOTICE.txtcarries the licence and the changes made. Credited in the README.canlab/core/n2k_db.pydecodes from it. Validity comes from each field's own range in the table, so reserved, error and not-available codes are never readings, signed fields included (0x7FFFis not available;0xFFFFis -1). Kelvin becomes °C, dates become ISO.decode_n2kkeeps the hand-written decoders first and falls back to the table. Fast-packet PGNs are decoded only from a reassembled message (reassembled=flag, threaded throughdecode_pgnand the multi-frame summary).package-data) and the binary (canlab.spec).Checked against real data
On the real marine recording, where both decoders exist they agree on every shared value: 800 headings, 400 positions, 400 wind readings, 200 rates of turn, 200 COG and SOG, 60 satellite counts, the GNSS fix after reassembly. Decoded PGNs on that bus go from 11 to 21 of 29; the rest are network management, group function and proprietary.
Found on the way
Both decoders rounded every value to six decimal places: a rate of turn of -0.0001047 rad/s read as -0.000105, and a 1e-7 degree position was cut to about ten centimetres. Values now round to their own resolution.
Tests
tests/test_n2k_db.py: agreement on the verbatim marine frames and the reassembled GNSS fix; the reserved, error and signed not-available codes; the fast-packet guard; a fast packet the hand table does not know, reassembled end to end; repeating groups; proprietary naming; the licence shipping with the table.pytest -q: 735 passed.acceptance_new_sources.py: 57/57. ruff clean.