gnss-gps-integrationlisted

# GNSS GPS Integration ## Overview Use this skill to connect a GNSS/GPS module to an MCU over UART and turn raw output into a trusted fix. The hard parts are proving the byte stream is intact (NMEA XOR checksum, UBX sync), rejecting invalid fixes, and getting acceptable TTFF given antenna, sky view, and backup-power constraints. ## When To Use Use this skill when: - The user integrates u-blox `NEO-M8N`, `NEO-M9N`, `MAX-M10`, or Quectel `L76`/`L80`/`LC76` over UART. - The work involves parsing `$GxGGA`, `$GxRMC`, `$GxGSA`, `$GxGSV`, the `*hh` XOR checksum, or the UBX binary protocol (`0xB5 0x62`, `UBX-NAV-PVT`). - Symptoms include no satellites, TTFF too long, `RMC` status `V`, lat/lon of 0, truncated NMEA frames, or PPS not toggling. - Configuration uses the legacy `UBX-CFG-PRT`/`UBX-CFG-MSG` messages (M8-era), the config-key interface `UBX-CFG-VALSET`/`UBX-CFG-VALGET` (M9/M10), or PMTK sentences (`PMTK251`, `PMTK220`, `PMTK314`). Do not use this skill when the UART link itself is unproven; confirm bytes arrive at the correct baud first. ## First Questions Ask for: - Exact module and vendor (u-blox M8/M9/M10 vs Quectel Lxx), since protocol and config differ. - UART baud (u-blox default `9600`, Quectel L76 default `9600`), wiring (TX/RX crossed, CMOS 3V3 levels). - Active vs passive antenna, its supply/bias-T, and current sky visibility (indoors vs open sky). - Backup power: is `V_BCKP`/RTC battery or supercap fitted, or does the module lose power fully each cycle? -