Real-Time Inertial Motor Controller (GD32V RISC-V)

A fault-tolerant, event-driven motor control system on the GD32V (RISC-V) Longan Nano. Featuring a custom non-blocking driver for the LIS2DW12 accelerometer capable of automatic bus recovery during EMI events.

Overview

This project demonstrates a robust embedded architecture using FreeRTOS and the Active Object pattern. The core focus was to create a "crash-proof" sensor driver that can recover from I2C bus lockups caused by DC motor electrical noise (EMI) without resetting the entire microcontroller.

It serves as a study in concurrency, hardware abstraction, and fault-tolerance on the RISC-V architecture.

Hardware

• MCU: Sipeed Longan Nano (GD32VF103CBT6 - RISC-V)
• Sensor: LIS2DW12 3-Axis Accelerometer
• Actuator: Standard DC Motor via DRV8833 H-Bridge
• Wiring: No custom PCB was used; modules are connected via breadboard for prototyping.

Module	Pin	Function
I2C sensor	PB6	SCL
	PB7	SDA
Motor Driver	PB0	PWM (Timer 2 CH2)
	PB1	PWM (Timer 2 CH3)
Debug	PC13	Status LED

Software Architecture

The system runs on FreeRTOS with two primary Active Objects (Tasks) communicating via a thread-safe Queue:

1. Sensor Actor: Polls the accelerometer every 20ms and converts raw tilt vectors into velocity commands.
2. Motor Actor: Receives commands and updates the PWM duty cycle. It implements a failsafe timeout: if no new data arrives for >100ms (due to sensor failure), the motor performs an emergency stop.

Fault-Tolerant Driver Design

The LIS2DW12 driver was written from scratch to handle I2C Bus Lockups. Standard drivers often hang in infinite while loops if a motor spark corrupts the clock line. This driver uses macro-based timeouts to detect these hangs and trigger a peripheral reset.

Key Implementation Details:

#define I2C_TIMEOUT_CYCLES 100000

/* Robust Wait Macro: Returns error (-1) instead of hanging forever */
#define I2C_WAIT_FLAG(instance, flag) \
    { \
        volatile int32_t timeout = I2C_TIMEOUT_CYCLES; \
        while (!i2c_flag_get(instance, flag)) { \
            if (--timeout <= 0) return -1; /* ABORT TRANSACTION */ \
        } \
    }

If I2C_WAIT_FLAG returns -1, the Sensor Actor initiates a Software Reset sequence on the I2C peripheral to clear the bus and resume operation automatically.

Build & Flash

This project uses the GD32V Linux toolchain.

1. Clone repository into your projects folder.
2. Put the Longan Nano into DFU Bootloader mode.
3. Compile and flash:

make dfu

Demo

compressed-out-tilt-motor.mp4

This video demonstrates real-time motor velocity control based on accelerometer tilt vectors.

Key Feature Showcase: Fault Injection & Recovery The video specifically highlights the system's robustness against connection failures:

1. Signal Loss: The I2C lines (green wires) are physically disconnected while the motor is running.
2. Failsafe Activation: The system detects the timeout immediately, triggering an Emergency Stop (Motor Speed = 0) and entering an error state (Blinking LED).
3. Automatic Recovery: Upon reconnection, the driver detects the restored bus, re-initializes the sensor, and resumes normal operation without requiring a hard reset.

Acknowledgements

• Based on the open-source GD32V Examples by Linus Remahl.