STAG 12 GPS Node — Live Lap Timing System

Real-time lap and segment timing for Formula Student, broadcast live to the in-car dash.

The SUFST STAG 12 GPS node is a standalone sensor module that transforms raw GNSS, IMU, and magnetometer data into precision-engineered lap/segment times, on the car, as you drive. Gates are persistent and reproducible across power cycles, broadcast live to the dashboard, and accurate to sub-millisecond resolution via GPS-time synchronization.

Feature	Spec
Timing accuracy	~1 ms (fused 104 Hz state with GPS-time stamping)
Lap detection	Automatic gate crossing, steering-wheel programmable (short/long/very-long press)
Gate persistence	Stored as absolute lat/lon, reproducible after power-cycle-and-move
Broadcast	20 Hz position/velocity, 50 Hz attitude, 100 Hz IMU, ~5 Hz gates, 1 Hz GPS/UTC time, CAN 1 Mbps
GNSS	u-blox ZED-F9P (GPS + Galileo, 20 Hz)
IMU	LSM6DSO32 accel+gyro + IIS2MDC magnetometer, 104 Hz
Hardware timing	Steering-wheel button edge-stamped by GPS receiver (nanosecond precision)
MCU	STM32G431 (170 MHz Cortex-M4F, 128 KB flash, FreeRTOS)

What's included

• Firmware — STM32G431 application with sensor fusion (Mahony AHRS + 6-state Kalman filter), lap-gate crossing detection, CAN broadcast, and persistent gate storage
• Dashboard tool — Python/PyQt6 desktop reference implementation: live telemetry plot, track map with gates, lap timing display, remote gate control
• CAN database — GPS.dbc message definitions for the car's CAN network
• Tests — Host-side unit tests for fusion, protocol, timing logic (no hardware needed)

For drivers

→ See DRIVER_GUIDE.md for how to set/clear gates and use the timing system.

For engineers

• QUICK_START.md — Get the firmware building in 5 minutes
• DEVELOPER.md — Detailed development environment, build system, testing, debugging
• ARCHITECTURE.md — Technical deep dive: sensor fusion, lap timing, CAN protocol, persistence
• DATASHEET.md — Component specs, pinouts, electrical, CAN matrix, firmware metrics

Hardware

The GPS mainboard (pcb/gps-mainboard) is a 2-layer, 65 mm × 85 mm board that:

• Talks to the car via 1× CAN-S (1 Mbps sensor bus), 1× RS232 (NMEA out to the MoTeC datalogger, RTCM corrections in for RTK), 1× steering-wheel button
• Synchronises to GPS time via a 1 PPS input from the ZED-F9P
• Runs 104 Hz IMU samples through a real-time fusion pipeline
• Persists gate configuration in the STM32's internal flash

See DATASHEET.md for schematics, layout, pinouts, and electrical specs.

Status

Production-ready firmware. Every module builds and links correctly; all unit tests pass. The system has been validated in simulation (realistic car dynamics, synthetic tracks) and field-tested for timing accuracy, lap detection, and gate persistence. Ready for track deployment in STAG 12.

Building

Firmware (target hardware)

Requires arm-none-eabi toolchain (GCC 13.x+ recommended):

cmake --preset Release
cmake --build --preset Release
# Output: build/gps_firmware.elf, ~58 KB

Debug build (with -O0):

cmake --preset Debug
cmake --build --preset Debug
# Output: ~94 KB (still fits in 128 KB CB variant)

Unit tests (host machine)

Runs on native compiler (no ARM toolchain needed):

cmake -B build-host -DGPS_HOST_TESTS=ON -G Ninja
cmake --build build-host
ctest --test-dir build-host
# 11/11 tests: UBX parsing, CAN pack/unpack, fusion, timing, persistence

Dashboard (reference UI)

cd tools/dashboard
pip install -e .
gps-dashboard

Contributing

Contributions follow SUFST style: read DEVELOPER.md for naming, testing, and commit conventions before opening a PR.

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Questions? Check ARCHITECTURE.md for the big picture, DEVELOPER.md for build/test details, or grep the codebase—comments are sparse by design (signal-to-noise, not mystique).

Last updated: 2026-07-05. SUFST STAG 12 GPS Node Firmware.