Linux-device-driver-

A simple linux device driver that can be run on both x86 and edge device (specifically most compatible with Raspberry Pi) as Rpi 's OS is easier to configure Tested on a normal linux system as well.

note: GPIO drivers are specific to Rpi / Any other SBC with similar numbering

Overview

This project contains Linux kernel modules developed from scratch for the Raspberry Pi 4B. It includes:

• A basic character device driver
• A GPIO control module for toggling LEDs via sysfs
• Drivers for usb

Designed to demonstrate low-level interaction with Linux kernel space using loadable kernel modules (LKM), targeting embedded systems and hardware-near control.

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⚙️ Technical Stack

• Platform: Raspberry Pi 4B (64-bit Debian OS), Ubuntu 24.04 LTS
• Language: C
• Kernel Version: 5.x
• Interfaces: insmod, sysfs, udev, /dev/
• Tools: make, modprobe, dmesg, cat, echo

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🛠️ Features

• Registers a custom char device in /dev/rpi_drv
• Supports basic open, read, write, close ops
• Controls a user-defined GPIO pin via sysfs
• Cleanly handles module_init and module_exit

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Setup:

1. sudo apt update

2. sudo apt upgrade -y

3. sudo apt install -y raspberrypi-kernal-headers

   // for installing the kernal headers

4. sudo apt install -y build-essential

5. sudo reboot

   //for opening of a fresh kernel

// 4. is necessary as we are running c scripts therefore it requires gcc , make (most probably preinstalled)

Then check the conents of the build folder:

after the running of the initial kernel:

Loading and unloading:

the generated .ko file can be used to load/ unload the kernel module (lkm):

Number:

• for chosing of a number , it should be a number that was not listed in ls proc/devices

• Kernel modules can register block or character devices (in the traditional unix sense, "device" is a word with many meanings) in the kernel, using a routine like register_blkdev together with a string that is supposed to identify the device.

• It's possible to use any string for that purpose, and these strings show up in the /proc/devices file (which is just a textual representation of this kernel table).

• //which are different from the major and minor numbers shown in /dev

• After the generation of device number and loading , it can be checked by

• cat /proc/devices | grep my_device_nr

$ ls /dev/ -al

shows the device in the list after the creation of the node . cat /proc/devices doesnt confirm the device creation (node) only the number associted.

Reading after the creation of device:

So the loading of the .ko file (lkm) of the corresponding device is necessary for the accessing of that device for either read/write

• initially when the corresponding kernel module for major no. 90 was not loaded but for 104 , it is unable to access the file.

output messages:

Issues: https://www.notion.so/Issues-16b3175a5f4380b3bb9fc1a1f0b49a01

Read Write :

shows the output response when the read_write LKM is loaded into the kernel.

So a dummy driver with a major number of 234, minor 0 is registered in the list of device drivers.

calling it by the node name given in the program (otherwise had to be made by the sudo mknod c/b command. and changing permissions.

writing and reading the contents of the driver.

output logs generated:

USB Device drivers:

1. For some reason the connection and the removal is detected only once -> directly from continuous dmesg ->matched on vendor id and product ID.

The collected message for registering the device -> During insertion of the kernel module.