BeagleBone Black LED Control Kernel Module (bbb_led)

A Linux character device driver (/dev/bbb_led) designed for the BeagleBone Black (TI AM3358). It exposes a user-space file interface to control onboard LEDs without hardware resource conflicts by integrating directly with the Linux Kernel LED Trigger Subsystem (led_trigger_event).

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🛠️ Prerequisites & Features

Prerequisites (Debian)

Ensure your BeagleBone Black is running Debian and has the matching Linux kernel headers installed before building out-of-tree kernel modules:

# Update package index
sudo apt update

# Install build essentials and matching kernel headers for Debian
sudo apt install -y build-essential linux-headers-$(uname -r)

🛠️ Features

• Safe User-Kernel Data Transfer: Uses copy_from_user and copy_to_user to interact safely across protection rings.
• Kernel Trigger Integration: Bypasses direct GPIO pin lockups by utilizing the kernel's native led_trigger framework.
• Safe Buffer Operations: Utilizes snprintf to prevent stack buffer overflow conditions inside the kernel space.

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🚀 Getting Started

1. Build the Kernel Module

Compile the driver against your running kernel headers:

make

2. Load the Module & Create Device Node

Insert the compiled module into kernel space, create its associated character device node, and set access permissions:

# Insert module into the kernel
sudo insmod bbb_led.ko

# Create the character device node (Major 240, Minor 0)
sudo mknod /dev/bbb_led c 240 0

# Grant read/write permissions
sudo chmod 666 /dev/bbb_led

3. Bind the LED Trigger

Assign the driver's custom trigger (bbb_control) to the USR3 LED:

echo bbb_control | sudo tee /sys/class/leds/beaglebone:green:usr3/trigger

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🧪 Usage & Testing

Interact with the hardware device via standard user-space file operations:

# Turn ON the USR3 LED
echo "1" > /dev/bbb_led

# Check current LED status
cat /dev/bbb_led

# Turn OFF the USR3 LED
echo "0" > /dev/bbb_led

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🧹 Cleanup & Unload

Restore default system states, remove the device node, and unload the kernel module:

# Reset LED USR3 trigger back to default
echo none | sudo tee /sys/class/leds/beaglebone:green:usr3/trigger

# Remove device node
sudo rm /dev/bbb_led

# Unload kernel module
sudo rmmod bbb_led

# Clean build artifacts
make clean