# XIAO ESP32-C6 Sensor Node Protocol

The XIAO sensor node reads the BNO086 and MAX-M10S and publishes vehicle telemetry over half-duplex RS485 at 115200 8-N-1, one JSON object per line. It owns no control state. Cargo remains the controller, HTTP server, and `/api/v1` source of truth; JBD/NimBLE behavior is unchanged.

The expansion-board pins are D2 driver enable, D4 TX, and D5 RX. Only physical bus ends should be terminated. Confirm A/B polarity because vendor labels vary.

## Schema version 1

`sensor_status` includes `node_id`, `firmware_version`, `uptime_ms`, and:

- `imu`: `online`, `valid`, `accuracy`, quaternion, yaw, pitch, and roll in degrees.
- `gps`: `online`, `fix`, satellites, latitude, longitude, altitude meters, speed kph, course degrees, and structured UTC.

Consumers must check `valid` or `fix` before displaying measurements and ignore unknown fields. The native breakout coordinate frame is reported initially; installation-specific axis remapping should follow physical calibration.

This link does not replace dashboard-to-Cargo WiFi/HTTP. A future dashboard receiver may display this telemetry without moving relay, BMS, alarm, or configuration authority away from Cargo.