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 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.
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.
