Linux Kernel Timer Driver

Overview

This project implements a custom Linux kernel platform driver that enables time-controlled string output using the Raspberry Pi system timer. The driver integrates interrupt handling, blocking I/O, and device tree configuration to provide a controlled interaction between user space and kernel space.

The core functionality allows a user to write a string to the driver, after which a blocking read operation waits for a timer interrupt before returning the stored data.

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Objectives

• Implement a Linux kernel platform driver
• Configure and use the Raspberry Pi system timer via Device Tree
• Enable interrupt-driven execution
• Support blocking read operations using wait queues
• Provide user-space interaction through a misc character device
• Ensure proper synchronization of shared resources

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Functional Description

The driver operates as follows:

1. A string is written to the device using the write() system call
2. The read() system call blocks until a timer interrupt occurs
3. The timer interval is configured via ioctl()
4. When the timer reaches the configured value, an interrupt is generated
5. The interrupt handler:
   • Clears the interrupt status
   • Updates the compare register for the next interval
   • Wakes up the blocked process
6. The read() call returns the stored string to user space

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System Architecture

The implementation consists of the following components:

• Platform Driver
  Responsible for binding the driver to the hardware defined in the Device Tree

• Misc Character Device
  Provides a simple interface for user-space interaction (/dev/timer)

• Interrupt Handler
  Handles timer interrupts and coordinates execution flow

• Wait Queues
  Used to block and wake processes during read operations

• Synchronization Mechanisms
  Spinlocks and/or mutexes are used to protect shared resources

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Device Tree Configuration

A custom Device Tree Source (DTS) file is created based on the Raspberry Pi 2 configuration:

bcm2709-rpi-2-b-custom.dts

The following properties are defined:

• Timer node within the soc node
• Base address and register size (reg)
• Interrupt lines (TIMER0–TIMER3)
• Clock frequency (1 MHz)
• Compatible string for driver binding

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Project Structure

linux-kernel-labs/
├── modules/
│   └── timer/
│       ├── timer.c
│       ├── Makefile
├── dts/
│   └── bcm2709-rpi-2-b-custom.dts
├── README.md

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Build and Execution

Build the module

make

Insert the module into the kernel

insmod timer.ko

Remove the module

rmmod timer

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Usage

Write a string to the device

echo "Test string" > /dev/timer

Read from the device (blocking)

cat /dev/timer

The output will be returned only after the configured timer interval expires.

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Synchronization and Concurrency

Due to the concurrent execution between interrupt context and user-space operations, shared resources must be properly protected. This is achieved using synchronization primitives such as spinlocks or mutexes, ensuring data consistency and preventing race conditions or deadlocks.

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Key Concepts

• Linux Kernel Modules
• Platform Drivers
• Misc Devices
• Interrupt Handling
• Wait Queues
• Device Tree
• Memory-Mapped I/O

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Notes

• The Linux kernel source is not included in this repository due to its size and availability as an external dependency
• Only custom driver code and configuration files are provided

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Author

Nina Dragićević Faculty of Technical Sciences, Novi Sad Department of Computer Engineering and Communications

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License

This project is intended for educational purposes only.