SVEA Low-Level Interface (Zephyr)

Firmware for the SVEA low-level interface running Zephyr 4.1.0 on the MikroE Clicker 4 for STM32F745VGT6. It bridges vehicle actuators, power management, sensors, and a micro-ROS agent on the host PC.

Highlights

• Servo control for steering, throttle/ESC, gearbox, and both differential locks with watchdog supervision and throttle slew limiting.
• SBUS input on USART2 with override/mute support and RC state export to ROS.
• micro-ROS publishers for IMU, encoder odometry, INA3221 rail telemetry, battery state, and RC feedback plus subscribers for drive commands.
• TI BQ769x0 battery management integration (alert, wake, SoC indication, peak tracking).
• Devicetree overlays pin out the Clicker 4 peripherals (PWM, I²C, GPIO) used by the application.

Repository Layout

• Projects/svea-lli/ – Zephyr application (sources, headers, Kconfig, overlays).
• modules/ – extra ported Zephyr modules (micro-ROS transport, BMS helpers). see micro_ros_zephyr_module and libresolar
• drivers/ – local driver glue compiled into the app.
• west-manifest/west.yml – locks Zephyr v4.1.0 and companion modules.

Prerequisites

• Zephyr SDK 0.16.x (or matching GCC toolchain) and CMake ≥ 3.20.
• Python 3.10+ with west installed (pip install --upgrade west).
• ROS 2 Iron (or newer) with the micro_ros_agent package on the host computer.
• MikroE CodeGrip Suite to flash the Clicker 4 board.

Setup

Check github action for environment setup. I use the zephyr ide extension.

Build

west build -b clicker4_stm32f7 Projects/svea-lli --pristine

Artifacts: build/zephyr/zephyr.hex (flash), build/zephyr/zephyr.elf (debug). Drop --pristine for incremental rebuilds.

Flash (CodeGrip GUI)

1. Open CodeGrip Suite and connect to the Clicker 4.
2. Program → Browse → select build/zephyr/zephyr.hex.
3. Enable Erase + Verify; press Write.
4. Reset/power‑cycle; the board appears as USB CDC (/dev/ttyACM*).

ROS Topics

Topic	Direction	Type	Notes
/lli/ctrl/steering	Subscribe	std_msgs/msg/Int8	−127…127 maps to 1000–2000 µs.
/lli/ctrl/throttle	Subscribe	std_msgs/msg/Int8	−127…127 maps to 1000–2000 µs.
/lli/ctrl/high_gear	Subscribe	std_msgs/msg/Bool	High gear request.
/lli/ctrl/diff	Subscribe	std_msgs/msg/Bool	Differential lock (front+rear).
/lli/remote/steering	Publish	std_msgs/msg/Int8	RC steer mirrored to ROS.
/lli/remote/throttle	Publish	std_msgs/msg/Int8	RC throttle mirrored to ROS.
/lli/remote/high_gear	Publish	std_msgs/msg/Bool	RC gear switch state.
/lli/remote/override	Publish	std_msgs/msg/Bool	true when RC override/mute is active.
/lli/remote/connected	Publish	std_msgs/msg/Bool	RC link health.
/lli/sensor/imu	Publish	sensor_msgs/msg/Imu	ISM330DLC data.
/lli/sensor/encoders	Publish	geometry_msgs/msg/TwistWithCovarianceStamped	Wheel odom → twist.
/lli/sensor/ina3221	Publish	std_msgs/msg/Float32MultiArray	[V, I, P] for ESC, 12 V, 5 V.
/lli/battery/state	Publish	sensor_msgs/msg/BatteryState	Pack voltage, current, SOC, flags.

No services/actions are exposed.

Hardware Wiring Summary

Use this with Projects/svea-lli/boards/clicker4_stm32f7.overlay, the official MikroE schematic, and wiring-guide-by-li-chen.pdf. Safest is to cross‑reference each overlay pin with the schematic before wiring.

Actuators (servo rail)

Function	MCU pin / timer	Board ref	Note
Steering	PE5 / TIM9_CH1	Servo P3	5 V rail.
Throttle/ESC	PE6 / TIM9_CH2	Servo P4	Ramp limited.
Gear	PB9 / TIM4_CH4	Servo P2	3‑position.
Diff front	PB5 / TIM3_CH2	PB5 pad	Use servo 5 V/GND.
Diff rear	PA2 / TIM5_CH3	Servo P5	5 V rail.

Remote control

Signal	MCU pin	Board ref	Note
SBUS	PA3 / USART2_RX	mikroBUS1 RX	Inverted SBUS; power from 5 V/GND.

Sensors (I²C2 + GPIO)

Peripheral	MCU pins	Board ref	Note
ISM330DLC IMU	PB10 SCL, PB11 SDA, PC15 RST, optional PD0 INT	mikroBUS1 SCL/SDA/RST/INT	Enable INT in overlay if wired.
INA3221	PB10 SCL, PB11 SDA	mikroBUS1 SCL/SDA	5 V supply.
Wheel enc L	PB2	PB2 pad	5 V/GND supply.
Wheel enc R	PC7	PC7 pad	Debounced in firmware.

Battery management (I²C1 + control)

Signal	MCU pin	Board ref	Note
BMS I²C SCL	PB6	MB2_TX / PB6	Pull‑ups on BMS.
BMS I²C SDA	PB7	MB23_RX / PB7	—
ALERT	PD6	D6	Active‑high.
PCHG gate	PD2	D2	Drives BQ76200.
TS1 wake	PD5	D5	Used by wake_chip.c.
SoC button	PE10	BTN1	Optional.

For anything else, match overlay pins to the schematic/silkscreen before wiring. The PDF is a quick reference during bring‑up.

Development Tips

• west build -t menuconfig for quick Kconfig tweaks; keep overlays under Projects/svea-lli/boards/.
• Console logs: USB CDC at 115200 baud (minicom -D /dev/ttyACM0 -b 115200).
• Recommended VS Code extension: Zephyr IDE (Mylonics): https://marketplace.visualstudio.com/items?itemName=mylonics.zephyr-ide

micro-ROS Agent Reminder

Start the agent on the host before launching ROS nodes:

ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyACM0 -b 115200

Adjust /dev/ttyACM* if your system enumerates differently.