Module nmea 

NMEA 0183 sentence assembly and parsing.

Every receiver in the tree speaks the same handful of sentences, so this is the one parser and each board contributes only its power sequencing. Four sentence types carry everything UMSH wants:

• RMC — the time, the date, and whether the fix is valid. The only sentence carrying a date, which is why it is the one that can set a wall clock.
• GGA — fix quality, altitude, and satellites in use.
• GSA — whether the solution is two- or three-dimensional, and the dilution of precision.
• GSV — satellites in view.

Integers only

No floating point anywhere. Latitude and longitude are parsed into i32 at 1e-7 degrees, which resolves about 11 mm — two orders finer than the 7-byte location encoding needs, and exact, so a position never shifts by a rounding step between the receiver and the wire. Parsing ddmm.mmmm in binary floating point would introduce error before the encoder ever saw the value.

What is not checked

Sentences whose checksum fails, whose fields are malformed, or whose talker is unknown are dropped silently. A receiver emits a torn line on every power-up and whenever the UART resynchronizes, and treating that as an error condition would mean reporting a fault on every cold start.

Structs

Assembler

Assembles bytes from a UART into complete sentences.

Gga

The GGA sentence.

Gsa

The GSA sentence.

Gsv

The GSV sentence.

Rmc

The RMC sentence.

Enums

Sentence

One parsed sentence, reduced to what UMSH uses.

Constants

DEGREE_SCALE

Latitude and longitude scale: 1e-7 degrees per unit.

MAX_SENTENCE

Longest NMEA sentence accepted, including $, the checksum, and the line terminator.

Functions

parse

Parse one sentence body: everything between the $ and the line terminator, checksum included.