Embedded Linux device drivers

Embedded devices need to interact with the real world somehow. Maybe using standard interfaces such as i2c, SPI, USB or maybe using low level interfaces such as GPIO, PWM, Analog to Digital and Digital to Analog. In all cases the link between Linux and the hardware is a device driver.

This course shows how to write several different types of device drivers for Linux, with an emphasis on the techniques that are applicable to embedded systems such as platform independence, cross development and efficient use of resources. The lab exercises are cross-compiled and tested on a typical development board, the BeagleBone Black (we can accommodate other hardware at your request).

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Duration

4 days

Price

£2000 (excluding VAT)

Upcoming courses

None scheduled: contact us to request a quote

Prerequisites

Essential

  • good understanding of the C language

Recommended

  • familiarity with Linux development and command-line tools

Materials

Copies of the presentations and lab notes, plus sample code and worked solutions for the labs.

Hands-on labs

An essential part of the training are the lab sessions, which take approximately 50% of the time. We normally work in pairs using a modern development board such as the Beaglebone. Each group will also need a laptop or desktop to run the system development tools. We will provide a bootable USB memory stick with an appropriate version of Linux and cross tool-chain so there is no need to install Linux beforehand.

Outline

Developing for embedded Linux

  • Getting and configuring a cross toolchain
  • Linux bootloaders: U-Boot

The Linux kernel

  • Where to get the kernel source
  • Board support packages
  • Kernel configuration options
  • Building and loading a kernel

Kernel modules

  • Writing a module and compiling "out of tree"
  • Loading and testing on the target
  • Passing parameters
  • Modules and the GPL license

Device driver basics

  • Types of device driver
  • Different ways for applications to interact with the driver
  • Character drivers
  • Building and testing a simple “misc” character device driver

Kernel debugging

  • Review of printk and the magic sysrq key
  • Interactive debugging using kgdb
  • What to do when the board won't boot

Sysfs and proc

  • Classes of driver: /sys/class
  • Driver attributes
  • Extending the proc file system

Wait queues and completions

  • Waiting for things to happen: wait queues
  • One-shot events: completions

Kernel locking

  • Mutual exclusion using kernel mutexes
  • Spinlocks
  • Atomic operations

Advanced character driver functions

  • Notifying events: poll and fasync
  • Driver specific interfaces: ioctl

Time and timers

  • Getting the system time: high resolution timers
  • Delays and sleeps
  • Kernel timers

Interrupts

  • Installing an interrupt handler
  • Synchronising using using spin_lock_irq
  • Deferred processing using tasklets and work queues

Accessing hardware

  • Memory regions
  • Allocating and freeing memory
  • Overview of device tree and how to extract information from a device tree
  • Mapping in device memory: ioremap
  • DMA buffers: coherent and stream mappings
  • Memory barriers

Sharing memory

  • mmap: sharing device registers
  • mmap: sharing DMA buffers
  • get_user_pages: how to access user memory