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M2 step 1: gnss probe finds the receiver on RX 15 / TX 13 at 115200

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A temporary `gnss probe` command listens on both pin orders at 115200
and 9600. Only RX 15 / TX 13 at 115200 carries NMEA, as Meshtastic's
board file says; M5Stack's GPIO 8/9 are the keyboard's I2C bus. The
output format (NMEA 4.10, GSA system IDs, GSV per signal) is recorded in
docs/milestones/M2.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT
This commit is contained in:
twisla
2026-10-04 22:05:01 +02:00
co-authored by Claude Opus 5.5
parent 9c30d47982
commit f812c62a3d
2 changed files with 30 additions and 1 deletions
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docs/milestones/M2.md
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**Goal:** the device knows where it is and what time it is without a network: a GNSS Service in the background, a GNSS App with the position and a sky view of the satellites, the clock set from satellites when there's no NTP, and Tracks recorded to the SD card.
**Hardware:** the Cap LoRa-1262 carries an ATGM336H-6N (AT6668), multi-constellation (GPS, BeiDou, Galileo, GLONASS, QZSS), with a ceramic antenna. NMEA over UART, 115200 8N1. Meshtastic's board file for this hardware uses GPIO 15 (ESP32 RX) and 13 (TX); M5Stack's page names GPIO 8 and 9, which the keyboard controller already uses. Step 1 checks on the device.
**Hardware:** the Cap LoRa-1262 carries an ATGM336H-6N (AT6668), multi-constellation (GPS, BeiDou, Galileo, GLONASS, QZSS), with a ceramic antenna. NMEA over UART, 115200 8N1. **Measured (step 1, `gnss probe`): RX GPIO 15, TX GPIO 13, 115200 8N1**, as in Meshtastic's board file; M5Stack's page names GPIO 8 and 9, which are the internal I2C bus the keyboard controller sits on. Output is NMEA 4.10 style: `GN` RMC, VTG and GGA, one GSA per constellation with the system ID (1 GPS, 2 GLONASS, 3 Galileo, 4 BeiDou, 5 QZSS) in its last field, and a GSV sequence per constellation and signal (`GP`, `GL`, `GA`, …) with the signal ID last. RMC carries a time even without a Fix (status `V`), so only a Fix makes it trustworthy.
## Decisions (design round 2026-10-04)