SDV VCU HIL - Hardware-in-the-Loop Simulation for Software-Defined Vehicle VCU

Hardware-in-the-Loop (HIL) test bench for a centralized Vehicle Control Unit (VCU) implementing 4-Wheel Independent Steering (4WIS) and Torque Vectoring, validated in real time against a CarSim vehicle dynamics model driven by MATLAB/Simulink.

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1. Overview

A Software-Defined Vehicle (SDV) HIL test bench that validates a centralized VCU's motion-control algorithms against a physics-accurate vehicle model:

• A driver (steering wheel + pedal set) provides real-time input to the VCU.
• The VCU computes per-wheel steering angle and torque commands.
• Four zone controllers (STM32) actuate a stepper motor (steering) and DC motor (traction) per corner, and report back actual angle/speed.
• CarSim/MATLAB consumes that feedback, simulates the resulting vehicle motion and tire forces, and sends vehicle state back to the VCU closing the loop.

Branches

• main : all control logic (Torque Vectoring + 4WIS) runs on Linux, on the VCU's main core. No Cortex-M needed.
• ipc : control logic offloaded to the two Cortex-M4 cores (core 0 = Torque Vectoring, core 1 = 4WIS), communicating with Linux over RPMsg/IPC.

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2. Hardware Topology

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3. Data Flow

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4. Communication

UDP frames are __attribute__((packed)) C structs defined in main.h, shared with the Cortex-M4 firmware. IPC frames go over RPMsg character devices (/dev/rpmsg0 = core 0, /dev/rpmsg1 = core 1).

4.1 Endpoints

Node	Address	Port	Direction
VCU (Linux, rx_vcu)	—	VCU_PORT = 5055	Listens for frames from MATLAB
MATLAB (Host PC)	10.252.62.212	MATLAB_PORT = 4093	Receives frames from VCU
Zone Controller FL	10.252.62.51	5051	Receives frames from VCU
Zone Controller FR	10.252.62.52	5052	Receives frames from VCU
Zone Controller RL	10.252.62.53	5053	Receives frames from VCU
Zone Controller RR	10.252.62.54	5054	Receives frames from VCU

4.2 Steer & Pedal → VCU (USB)

Read by thread_steer_reader, buffered as steer_sample_t.

Field	Type	Description
brake	uint8_t	Brake pedal input
accel	uint16_t	Accelerator input, used downstream as Vx_des (desired speed)
steer	int16_t	Steering wheel angle
ts	struct timespec	Sample timestamp (CLOCK_MONOTONIC_RAW)

4.3 MATLAB → VCU (UDP, matlab_recv_frame_t)

Sent by CarSim/MATLAB to VCU_PORT (5055). Identified by header = MATLAB_FRAME_HEADER (0xAC) and id = MATLAB_FRAME_ID (0x05).

Field	Type	Description
header	uint8_t	Frame header, 0xAC
id	uint8_t	Frame id, 0x05
Vx	uint16_t	Vehicle longitudinal velocity
Vy	uint16_t	Vehicle lateral velocity
angWheel	uint16_t[4]	Actual wheel steering angle per corner
yawRate	uint16_t	Vehicle yaw rate
Fy	uint32_t[4]	Lateral tire force per corner
Fz	uint32_t[4]	Vertical tire force per corner
Vx_wheel	uint16_t[4]	Wheel longitudinal velocity per corner
seq	uint8_t	Sequence number

4.4 VCU → MATLAB — Brake (UDP, vcu_brake_matlab_frame_t)

Sent by the VCU to MATLAB (10.252.62.212:4093). Identified by header = MATLAB_BRAKE_HEADER (0xCA) and id = MATLAB_BRAKE_ID (0x06).

Field	Type	Description
header	uint8_t	Frame header, 0xCA
id	uint8_t	Frame id, 0x06
brake	uint8_t	Brake value forwarded from the driver's Steer & Pedal input
seq	uint8_t	Sequence number

4.5 VCU → Zone Controller (UDP, corner_send_frame_t)

Sent per-corner to each Zone Controller's IP/port (see 4.1). Identified by header = CORNER_FRAME_HEADER (0xCB).

Field	Type	Description
header	uint8_t	Frame header, 0xCB
id	uint8_t	Corner id (1 = FL, 2 = FR, 3 = RL, 4 = RR)
Tm_ref	uint16_t	Torque reference for this corner (from Torque Vectoring result)
Vx	uint16_t	Vehicle longitudinal velocity
Vx_wheel	uint16_t	Wheel longitudinal velocity for this corner
Vx_des	uint16_t	Driver-requested longitudinal speed
Ang_ref	uint16_t	Steering angle reference for this corner (from 4WIS result)
Mzd	uint32_t	Desired yaw moment (from Torque Vectoring result)
seq	uint8_t	Sequence number

4.6 VCU (Linux) ↔ Cortex-M4 Core 0 — Torque Vectoring (IPC, /dev/rpmsg0)

Linux → Core 0 (rpmsg_tv_in_t):

Field	Type	Description
Vx_des	uint16_t	Driver-requested longitudinal speed
Vx	uint16_t	Vehicle longitudinal velocity
Vy	uint16_t	Vehicle lateral velocity
angWheel	uint16_t[4]	Actual wheel steering angle per corner
yawRate	uint16_t	Vehicle yaw rate
Fy	uint32_t[4]	Lateral tire force per corner
Fz	uint32_t[4]	Vertical tire force per corner

Core 0 → Linux (rpmsg_tv_out_t):

Field	Type	Description
Tm_ref	uint16_t[4]	Torque reference per corner
Mzd	uint32_t	Desired yaw moment

4.7 VCU (Linux) ↔ Cortex-M4 Core 1 — 4WIS (IPC, /dev/rpmsg1)

Linux → Core 1 (rpmsg_fwis_in_t):

Field	Type	Description
steer_angle	uint16_t	Driver steering wheel angle (offset-encoded)
Vx	uint16_t	Vehicle longitudinal velocity

Core 1 → Linux (rpmsg_fwis_out_t):

Field	Type	Description
Ang_ref	uint16_t[4]	Steering angle reference per corner

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5. Component Details

VCU — Linux app (vcu/)

• thread_steer_reader - polls USB Steer & Pedal, updates double-buffered steer_sample_t
• thread_net_rx - receives UDP frames from MATLAB (matlab_recv_frame_t)
• thread_tv_rx / thread_fwis_rx - block on /dev/rpmsg0 / /dev/rpmsg1 for Cortex-M4 results
• thread_control - main dispatcher: builds IPC jobs, sends brake to MATLAB, fans out corner_send_frame_t to all 4 Zone Controllers

Cortex-M4 Core 0 - Torque Vectoring (sdk_master/cm4_core0/) FreeRTOS + RPMsg-lite. rpmsg_task ↔ Linux, tv_task runs Torque_Vectoring_step() → Tm_ref[4]/Mzd, monitor_task logs CPU/IO stats every 5s.

Cortex-M4 Core 1 - 4WIS (sdk_remote/cm4_core1/) FreeRTOS + RPMsg-lite. rpmsg_task ↔ Linux, fwis_task runs FWIS_Compute() → Ang_ref[4], monitor_task logs CPU/IO stats every 5s.

Host PC - MATLAB/Simulink + CarSim Runs the CarSim vehicle dynamics model, a PID torque controller, and the sensor/calculation block that returns Vx, Vy, yawRate, Fy[i], Fz[i] to the VCU each cycle.

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6. Deployment / Build Guide

Linux (Toradex Apalis i.MX8 — Yocto)

# Source the Yocto SDK environment
source <path-to-sdk>

# Generate the CMake toolchain file
./scripts/setup.sh

# Open in VS Code and build
code .

Cortex-M (core 0 & core 1)

# Install/point to the Arm GNU toolchain
export ARMGCC_DIR=<path-to-toolchain>

# Core 0 - Torque Vectoring
cd cortex-m/boards/mekmimx8qm/multicore_examples/rpmsg_lite_pingpong_rtos/sdk_master/cm4_core0/armgcc
./build_debug

# Core 1 - 4WIS
cd cortex-m/boards/mekmimx8qm/multicore_examples/rpmsg_lite_pingpong_rtos/sdk_remote/cm4_core1/armgcc
./build_debug

Boot image U-Boot & flashing

1. Build U-Boot from source - Toradex guide
2. Replace imx-boot in the os folder with your build - Toradex guide.
3. Toradex hardware setup - Toradex guide
4. Flash via Toradex Easy Installer (Tezi) - Toradex guide

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7. References

• Toradex Documentations - web
• IPC framework (rpmsg-lite) - repo