NMEA 0183 Driver

Overview

An in-house Java implementation of NMEA 0183 v4.x, the standard ASCII protocol used in the marine / shipboard / GNSS domains. Based on the publicly available NMEA association spec, Wikipedia, and general manuals. No external libraries or copied GitHub code.

Item	Value
`opc_type`	`NMEA`
Implementation class	`plantpulse.driver.protocol.nmea.NMEADriver`
Library	(none — in-house implementation, NMEA 0183 v4)
read	Good (based on the receive cache)
write	❌ (`isWriteSupported() = false`, receive-only)
Default port	`10110` (NMEA over IP de-facto)
Security	None

Physical medium

The NMEA 0183 standard specifies RS-232/RS-422 serial (4800 / 38400 baud), but in actual operation it is common for a multiplexer/gateway to forward the data over TCP or UDP as NMEA over IP. This driver accepts the TCP variant.

Classes / structure

NMEADriver  (BaseProtocolDriver)
 ├── Socket / BufferedReader   (US-ASCII)
 ├── receiverThread            — daemon, "NMEA-Receiver-<opc_id>"
 ├── lastByType                — ConcurrentHashMap<sentenceType, parsed map>
 ├── readLine()                — CR/LF 분리 + MAX_LINE_LEN(256) 가드
 ├── processLine(line)         — '$' / checksum 검증 / talker 제거 / 필드 split
 ├── addAliases(type, fields)  — RMC/GGA/GLL/VTG/GSA/GSV/HDT/HDM/MWV/DBT/DPT/MTW/VHW/ZDA/XDR
 └── xorChecksum(payload)      — '$' 와 '*' 사이 XOR

socket.setSoTimeout(0) — provided for serial emulation / low-speed equipment.

Wire format summary

$<talker><sentence>,f1,f2,...,fN*<CC><CR><LF>
예) $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A

2-character talker ID (GP/GL/GN/GA/HC/II/AI ...) + 3-character sentence type.
A proprietary P prefix is used as the cache key as-is, without talker separation.
*<CC> checksum = XOR of every char between $ and * (2-digit uppercase hex).
Length limit is 82 characters (NMEA 0183 v4 standard); this implementation guards with MAX_LINE_LEN=256.

Cache / read format

Messages that pass processLine() are stored in lastByType under the sentence type (e.g. RMC) key:

parsed = {
   "__raw__":  "$GPRMC,...",
   "__type__": "RMC",
   "1":        "123519",       // utc
   "2":        "A",            // status
   ...
   // alias
   "utc":   "123519",
   "lat":   "4807.038",
   ...
}

read("RMC.7") → field 7 (speed). read("RMC.lat") → alias.

OPC registration options

If options.nmea.port is present, it overrides the OPC opc_agent_port.

No connect-timeout / read-timeout options — CONNECT_TIMEOUT_MS = 5000, soTimeout = 0.

Tag address format

Notation	Meaning
`RMC.7`	Field 7 of the RMC sentence
`GGA.2`	Field 2 of GGA (latitude)
`RMC.utc` / `RMC.lat` / `RMC.lon` / `RMC.speed`	alias
`RMC`	Raw string (no field index / alias specified)

Supported sentences + aliases

Defined by addAliases():

type	alias examples
`RMC`	utc, status, lat, ns, lon, ew, speed, course, date, magvar, magvarew, mode
`GGA`	utc, lat, ns, lon, ew, fix, sats, hdop, alt, altunit, geoidsep, sepunit, dgpsage, dgpsid
`GLL`	lat, ns, lon, ew, utc, status, mode
`VTG`	cogtrue, cogmag, speed, speedkn, speedkm, mode
`GSA`	mode1, mode2, pdop, hdop, vdop
`GSV`	totalmsgs, msgnum, satsinview
`HDT` / `HDM`	heading, t / m
`MWV`	angle, ref, speed, units, status
`DBT` / `DPT`	depthft, depthm, depth, depthfa / depth, offset, max
`MTW`	temp, units
`VHW`	headingt, headingm, speed, speedkm
`ZDA`	utc, day, month, year, tzh, tzm
`XDR`	type, value, units, id (first group only)

Undefined sentences can still be accessed by 1..N index.

Supported / not supported

✅ Checksum verification ($~* XOR); lines are discarded on mismatch
✅ Automatic talker ID removal (e.g. GPRMC → RMC)
✅ Aliases for the 16 most commonly used sentences
✅ Proprietary $P... lines preserved as-is
❌ ! encapsulation (AIVDM and other AIS) — currently only $ is accepted
❌ Multi-message GSV accumulation
❌ write / sentence transmission

Test coverage

test/java/plantpulse/driver/protocol/nmea/

Class	Test count
`NMEADriverTest`	15
`NMEASpecTest`	22

37 tests in total — checksum, talker separation, alias mapping, index access, length limit.

References

NMEA 0183 v4 standard (publicly available NMEA association items)
Code: src/plantpulse/driver/protocol/nmea/NMEADriver.java

Overview​

Classes / structure​

Wire format summary​

Cache / read format​

OPC registration options​

Tag address format​

Supported sentences + aliases​

Supported / not supported​

Test coverage​

References​