Turbo ECU

self-drive RC

Demo

How?

Comma 3/3X/4 expects CAN. RC hardware speaks I2C/PWM. This bridges the gap: comma thinks it's talking to a car, ESC gets what it expects

Data path: comma <-CAN-> ECU <-PWM/I2C-> steering servo + ESC telemetry/control

No RTOS. No stdlib. 96 MHz Cortex-M4 running raw HAL

Get Turbo ECU

Join the waitlist at vapor.autos, then DM @simcity99 on X with your email to get early access

Hardware Requirements

Reference build: Arrma Typhon + Castle Creations Mamba X (should work with any RC + Castle ESC)

• Comma device (Comma 3/3X/4)
• Turbo ECU
• RC car with a Castle Creations ESC
• ST-LINK V2 (or compatible ST-LINK probe) for flashing Turbo ECU via SWD (make flash)
• Castle Link USB to flash/configure the ESC
• USB-to-UART adapter (FTDI/CP2102/CH340 or similar) only for UART debug output (make serial / make dev)

ESC Setup

Castle Link USB is used to flash/configure the ESC.
Castle Serial Link is a daughterboard on Turbo ECU and is the runtime I2C telemetry/control path used by firmware.

Before driving:

1. Connect the ESC to Castle Link USB.
2. Flash/update ESC firmware and apply required ESC settings.
3. Confirm Turbo ECU Castle Serial Link runtime settings:
   • I2C slave address: 0x08
   • I2C bus speed: 100kHz
   • For reversible/car ESC setups, fail-safe output at neutral (50 = 1.5ms) See protocol spec for details

Hardware

• PCB project (KiCad): pcb/ecu.kicad_pro
• ECU PCB assembly 3D model: mech/ecu.step
• Top case models: mech/top_case.step, mech/top_case.stl
• Bottom case models: mech/bottom_case.step, mech/bottom_case.stl

Specs

Interface	Protocol	Function
OBD-C	CAN	Steering/throttle in, speed out
Castle Serial Link (to ESC)	I2C	Throttle control, telemetry
Steering	PWM	Direct servo control
Headlights	GPIO	FET-switched
Debug	UART	printf output

LED Status	Meaning
Red	I2C connection to Castle Serial Link/ESC is bad
Blue	Comma CAN control traffic is active and healthy
Green	ECU running with I2C healthy but no recent comma CAN control traffic

CAN Message Contract

CAN ID	Name	Dir (ECU view)	DLC	Payload	Units / Notes
0x202	Steering Command	RX	2	int16 (little-endian)	Raw steering command (-18000..18000)
0x203	Throttle Command	RX	2	int16 (little-endian)	Raw throttle command (-10000..10000)
0x204	Headlights	RX	1	u8	0=off, 1=on
0x205	Cruise Enable Command	RX	1	u8	0=disabled, 1=enabled
0x205	Cruise Enable Status	TX	1	u8	Current ECU cruise state (0/1)
0x208	Steering Angle	TX	2	int16 (little-endian)	Raw steering angle feedback
0x209	Vehicle Speed	TX	2	uint16 (little-endian)	Speed in cm/s

All 16-bit CAN payload fields use little-endian byte order (LSB first)

Control watchdog: if no valid control CAN traffic is received for 500ms, throttle and steering decay to neutral

Loop Rates

Loop	Rate	Function
Main scheduler tick	1kHz	Runs time-sliced task checks and CAN RX processing
CAN telemetry TX	100Hz	Sends round-robin status frames (0x205, 0x209, 0x208)
Actuator update	50Hz	Writes steering PWM + Castle throttle command
Speed read	20Hz	Reads Castle speed register and updates CAN speed payload
Debug print	1Hz	UART runtime counters/state snapshot

Dev

First time setup

make install-deps  # Install system deps: clang-format, clang-tidy, ARM toolchain, openocd
make setup         # Create venv and install Python deps
make keys          # Generate signing keypair

If you are using hardware CAD/media assets (pcb/ecu.3d, mech/, demo media), run:

git lfs install   # One-time local Git LFS setup
git lfs pull      # Fetch LFS-tracked assets (CAD/media)

Build and flash

Activate the venv before running make commands:

source venv/bin/activate
make               # Build firmware
make flash         # Build and flash to device
make dev           # Flash and open serial monitor
make serial        # Open UART debug console

Other commands

make lint          # Run linters (ruff + clang-format)
make tidy-ci       # Run clang-tidy in CI mode (fails on errors)
make fmt           # Auto-format C code
make help          # Show all commands

Development

Release build

RELEASE=1 CERT=/path/to/cert make   # Production build with custom certificate

Project structure

board/          Firmware source code
  main.c        Main application loop
  bootstub.c    Bootstub (signature verification TODO)
  can.h         CAN message handling
  castle.h      I2C comms with Castle Serial Link
  inc/          STM32 HAL drivers and CMSIS headers
  obj/          Build artifacts (ELF/BIN and object files)
crypto/         RSA signature verification
docs/           Documentation
  turbo_ecu_pinout.md             Turbo ECU board-level pin assignments
  stm32f413_af_table.md           STM32F413 alternate-function reference
  castle_serial_link_protocol.md  Castle ESC I2C protocol spec
pcb/            Hardware design files
  ecu.kicad_pro KiCad project
  ecu.kicad_sch KiCad schematic
  ecu.kicad_pcb KiCad board layout
  ecu.pretty/   Custom footprints
  ecu.symbols/  Custom symbols
  ecu.3d/       Local 3D model assets referenced by KiCad
mech/           Mechanical CAD exports
  ecu.step      Full ECU assembly model
  top_case.*    Top enclosure model(s)
  bottom_case.* Bottom enclosure model(s)
tests/          Hardware test utilities

References

• Turbo ECU Pinout
• STM32F413 AF Table
• STM32F413CG Datasheet
• STM32 HAL Documentation
• Castle Serial Link Protocol

License

This project is licensed under the MIT License. See LICENSE.

TODO

• Enforce boot-time signature verification in bootstub.c before jumping to app
• Add anti-rollback version checks in bootstub
• Split debug/release key material (separate keypairs and trust policy)
• Verify Castle electrical-RPM to vehicle-speed conversion against measured ground truth
• Calibrate steering angle offset and update STEERING_ANGLE_OFFSET accordingly

Acknowledgments

• Firmware design inspiration from comma body
• Hardware design and KiCad workflow inspiration from OpenpilotHardware