This document provides an introduction to embedded Linux and device drivers. It defines an embedded system as a special-purpose computer designed to perform dedicated functions with real-time constraints, often embedded as part of a complete device. Linux is commonly used in embedded systems due to advantages like reuse of existing components, community support, and low cost. The document outlines the typical hardware and software requirements for developing embedded Linux systems, and provides an overview of the Linux kernel architecture for device drivers, including the unified device model, bus drivers, and platform devices.

1. Introduction to Embedded Linux
and Device Drivers
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2. What is an Embedded system?
An embedded system is a special-purpose computer
system designed to perform one or a few dedicated
functions, often with real-time computing constraints.
 It is usually embedded as part of a complete device
including hardware and mechanical parts.
In contrast, a general-purpose computer, such as a
personal computer, can do many different tasks
depending on programming.
Embedded systems control many of the common
devices in use today.

3. Embedded System Products

4. Linux
The Free Software and Open Source world offers a
broad range of tools to develop embedded systems.
Advantages
Reuse of existing components for the base system
Allows to focus on the added value of the product.
High quality, proven components (Linux kernel, C
libraries...)
Complete control on the choice of components
Modifications possible without external constraints
Community support: tutorials, mailing lists...
Low cost, in particular no per-unit royalties.
Potentially less legal issues.
Easier access to software and tools.

5. Linux Architecture
Hardware
Boot loader
Linux kernel
Standard C library
Library Library Library
Application
Tools

6. Embedded Hardware
Hardware for embedded systems is often different
from hardware for classical systems.
Often a different CPU architecture: ARM, MIPS or
PowerPC. Intel atom based on x86 arch is also used.
Storage on flash : NOR or NAND type, often with
limited capacity (from a few hundreds of MB to few
GB)
Limited RAM capacity (from a few tens of MB to
several hundreds of MB)
Many interconnect buses generally not often found
on the desktop: I2C, SPI, SSP, CAN, etc.

7. Minimum System HW Req
A CPU supported by gcc and the Linux kernel
32 bit CPU
MMU-less CPUs are also supported, through the
uClinux project.
A few MB of RAM (4 MB), 8 MB are needed to
really do something.
Linux isn't designed for small microcontrollers that
just have a few tens or hundreds of KB of flash and
RAM.
Base metal, no OS
Reduced systems, such as FreeRTOS , Nucleus

8. SW Comp’s Req for Development
Cross-compilation tool chain
Compiler that runs on the development machine, but
generates code for the target
Bootloader
Started by the hardware, responsible for basic
initialization, loading and executing the kernel
Linux Kernel
Contains the process and memory management,
network stack, device drivers and provides services to
userspace applications
C library
The interface between the kernel and the userspace
applications
Libraries and applications
Third-party or in-house

9. Driver Development
Kernel Architecture for Device Drivers
Embedded Linux Driver
Development

10. Kernel and Device Drivers
Application
System call interface
Framework
Driver
Bus infrastructure
Hardware
Userspace
Kernel

11. Unified Device Model
The 2.6 kernel included a significant new feature: a unified device
Model :
 Instead of having different ad-hoc mechanisms in the various
subsystems, the device model unifies the description of the
devices and their topology
 Minimization of code duplication
 Common facilities (reference counting, event notification,
power management, etc.)
 Enumerate the devices, view their interconnections, link
the devices to their buses and drivers, etc.
 Understanding the device model is necessary to understand
how device drivers fit into the Linux kernel architecture.

12. Bus Drivers
 The first component of the device model is the bus driver;
 One bus driver for each type of bus: USB, PCI, SPI, MMC, I2C, etc.
 It is responsible for:
 Registering the bus type (struct bus_type)
 Allowing the registration of adapter drivers (USB controllers,
I2C adapters, etc.), able of detecting the connected devices,
and providing a communication mechanism with the devices
 Allowing the registration of device drivers (USB devices, I2C
devices, PCI devices, etc.), managing the devices
 Matching the device drivers against the devices detected by
the adapter drivers
 Provides an API to both adapter drivers and device drivers
 Defining driver and device specific structure, typically
xxx_driver and xxx_device

13. Example: USB Bus
USB core
Registers the bus_type structure
USB adapter
driver A
USB adapter
driver B
USB device
driver 1
USB device
driver 2
USB device
driver 3
System
USB1
USB2
DEV1 DEV2
DEV3 DEV4 DEV5

14. Platform Devices
 On embedded systems, devices are often not connected
through a bus allowing enumeration, hot plugging, and
providing unique identifiers for devices.
 However, we still want the devices to be part of the device
model.
 The solution to this is the platform driver / platform device
infrastructure.
 The platform devices are the devices that are directly
connected to the CPU, without any kind of bus.

15. Linux DD Course Content
Overview
Understanding the Linux kernel
 Understanding the development process
 Kernel Internals
 Root file system development from scratch
 Developing Linux device drivers
 Driver architecture
 Development of char driver
 Working with the kernel development community
 Practical labs with ARM boards as well as emulated
PC systems
 Duration
 50 hrs
For further queries/enquiries contact :training@definecareer.com

16. Thank you!