Replace altitude-validity heuristic with authoritative GGA quality
field (SPS/DGPS/RTK) and GSA nav mode (2D/3D) via TinyGPSCustom
extractors. Send $PAIR062 commands at boot to filter NMEA output
to only GGA/GSA/RMC/GSV and configure PPS for fix-only pulses.
GpsPayload struct gains fix_quality field (16 -> 14 bytes packed).
The RYS352A uses Airoha AG3352 engine with $PAIR proprietary
commands. UBX is u-blox, PMTK is MediaTek — neither applies.
Also document TinyGPS++ v1.1 requirement for GN talker ID
(multi-constellation) support and reference the PAIR command guide.
The AG3352 GNSS engine in the RYS352A ships at 115200 8N1 per
the datasheet spec table. 9600 was a generic assumption that
would cause the UART to read garbage and never acquire a fix.
RYS352A GPS on UART2 (GPIO5/6) with PPS interrupt (GPIO7),
MPU-9250 IMU and BMP388 barometer on shared I2C bus (GPIO8/9).
Sensor data exposed via dedicated BLE service with binary
notify characteristics alongside the existing NUS serial bridge.
Sensors degrade gracefully if not wired.
MPU-9250 provides magnetometer (auto north alignment), accelerometer
(elevation verification), and gyroscope (slew quality). BMP388 provides
pressure and temperature for atmospheric refraction correction at low
elevation angles. Both share I2C bus on GPIO8/9.
NimBLE-based Nordic UART Service (NUS) bridge on ESP32-S3-DevKitC-1.
Transparent passthrough: BLE client writes → UART1 TX → RS-422 → G2,
and G2 → RS-422 → UART1 RX → BLE notifications. USB serial serves as
debug monitor and fallback input.
Uses two MAX485 modules (one locked TX, one locked RX) with a SparkFun
BSS138 level converter for 3.3V/5V translation. Wiring schematic and
RJ-12 pinout documented in docs/ble-bridge-wiring.md.
