HAL Across Domains: How Different Systems Define Hardware Abstraction Layers

Different domains define HAL differently based on their needs:

1. Autonomous Driving Domain Controllers

HAL Purpose: Abstract sensor and actuator hardware

Typical HAL Structure:

// Example concepts (not actual code)
class SensorHAL {
    // LiDAR abstraction
    virtual PointCloud readLiDAR() = 0;
    
    // Camera abstraction
    virtual ImageFrame readCamera(int camera_id) = 0;
    
    // Radar abstraction
    virtual RadarData readRadar() = 0;
    
    // GPS/IMU abstraction
    virtual PoseData readPose() = 0;
};

class ActuatorHAL {
    // Steering control
    virtual void setSteeringAngle(float angle) = 0;
    
    // Throttle/brake control
    virtual void setThrottle(float value) = 0;
    virtual void setBrake(float value) = 0;
    
    // Transmission control
    virtual void setGear(int gear) = 0;
};

Key Differences from LinuxCNC HAL:

• Focuses on sensor fusion and vehicle control
• Higher-level APIs (images, point clouds, vehicle commands)
• Handles complex sensor calibration, synchronization
• Often event-driven + periodic processing
• Safety-critical with redundancy

2. Robotics Frameworks (ROS, etc.)

HAL Purpose: Abstract robot hardware (motors, sensors, grippers)

Typical Structure:

// Example concepts
class RobotHAL {
    // Joint control
    virtual void setJointPosition(int joint_id, float position) = 0;
    virtual float getJointPosition(int joint_id) = 0;
    
    // Sensor access
    virtual SensorData readSensor(int sensor_id) = 0;
    
    // Actuator control
    virtual void setActuator(int actuator_id, float value) = 0;
};

Key Features:

• Joint space abstractions (similar to kinematics in LinuxCNC)
• Often uses middleware (ROS, DDS)
• Supports complex robots (humanoids, mobile bases, manipulators)

3. Embedded Systems (ARM Mbed, Arduino HAL)

HAL Purpose: Abstract microcontroller peripherals

Typical Structure:

// Example
class GPIO_HAL {
    void pinMode(int pin, Mode mode);
    void digitalWrite(int pin, bool value);
    bool digitalRead(int pin);
};

class SPI_HAL {
    void begin();
    void transfer(uint8_t data);
};

Key Features:

• Low-level peripheral abstraction (GPIO, UART, SPI, I2C, ADC)
• Very close to hardware
• Minimal overhead

4. Operating System HAL (Windows, embedded Linux)

HAL Purpose: Abstract platform differences (CPU, interrupt controller, DMA)

Functions (like Windows HAL.dll):

• Interrupt management
• DMA operations
• Processor initialization
• Bus operations
• Timer access

Key Features:

• Very low-level (kernel mode)
• Platform-specific implementations
• OS-level abstraction

Comparison Table

Key Insight

The term “HAL” is generic, and each system defines it for its domain:

1. What hardware needs abstracting? (LinuxCNC: motion hardware, Autonomous: sensors/vehicle)
2. What level of abstraction? (LinuxCNC: signal routing, Embedded: register access)
3. What operations are needed? (LinuxCNC: real-time control loops, Autonomous: sensor reading/actuator control)