Device Drivers Witawas Srisa-an

Device Drivers

• Witawas Srisa-an

• Embedded Systems Design and Implementation

Device Drivers

• What are device drivers?

• What are they used for?
• Why are they important?

Why Do We Need Drivers?

• Custom platforms

• Contain many peripheral devices and kernel (e.g. CE) supported CPU
• OAL development to get kernel to boot on the board
• Device drivers to allow applications to access peripheral devices

An Example

• To access a serial port in Windows CE

• calls CreateFile( ) on COMx
• calls WriteFile( ) to write some bytes of data to the serial port
• calls CloseHandle( ) to close the serial port.

Drivers in CE

• A driver is simply a dynamic-link library (DLL)

• DLLs are loaded into a parent process address space
• Run in user mode (different than most OSs)
• the parent process can then call any of the interfaces exposed from the DLL
• LoadLibrary( )
• LoadDriver( ) --- memory resident

Writing Device Drivers

• Most of the time spent on system integration is in this process

• Some devices have support on standard CE release and some don’t
• Onboard or installable
• Onboard devices may require platform dependent modification to the kernel image
• Installable devices may require code to be more platform independent
• Drivers APIs can also be used to provide application-level services

Device Driver Models

• Device drivers, over the years, have become very complex

• Drivers are separated into classes
• Serial, network, audio, video, touch panel, etc.
• Layer approach is used
• To support a new device, a layer is modified instead of rewriting the entire driver
• Processing functions required for a given class often do not require modification

Device Driver Architecture

Stream-Interface

• Allow accesses to an array of devices through basic file I/O interfaces

• Often used for installable devices
• The device manager (DM) manages stream-interface drivers
• DM operates as its own process
• Device driver DLLs are mapped into the address space

Other Driver Models

• Native Interface

• USB Interface

• Network Device Interface Specification

Device Driver Labs

• http://www.microsoft.com/downloads/details.aspx?FamilyID=486E8250-D311-4F67-9FB3-23E8B8944F3E&displaylang=en

• Download lab tools from the course website

• Create a simple Internet Appliance Windows CE project

• Create a device driver workspace and build the workspace

• Build OS image

• Attach the device

• Open prompt through build OS | Open Release Directory

• dumpbin –exports StreamDrv.dll