Final Presentation

Wireless LAN driver for Win CE

Eli Bendersky & Igor Oks

Supervisor: Yevgeny Rivkin

Project Goals

• Experience with Win CE based development

• Understanding the internals of a WLAN card driver

• Serve as a starting point for future projects based on communications using the 802.11 protocol

• Set up a functional WLAN environment

• Important: Extensive documentation

Overview

• Driver originally written by Symbol Technologies

• Handed over to Intel for further development

• Our laboratory received the sources from Intel to understand and improve the driver

Driver Development Models

• Monolithic – code consists of both platform dependent and platform independent code

• Layered – code is divided to platform independent code (usually common to all drivers) and platform dependent code

NDIS

• Network Driver Interface Specification

• Provides a fully-abstracted interface for network adapter device-driver development

Miniport Drivers

• Our driver is a Miniport driver

• A Miniport driver is wrapped with NDIS from both sides

• Higher level applications use NDIS calls to contact the driver

• The driver uses NDIS calls to connect to the underlying hardware

Driver Code

DriverEntry

• Primary initialization routine for the driver

• Initializes the wrapper and registers the miniport driver in the system

Demonstration: Sending mechanism

Interrupt Handling

• Hardware generates an interrupt whenever it reaches a state where software intervention is required

• The interrupt is handled by the Interrupt Service Routine (ISR)

IsrIsr

• This handler implements MiniportIsr

• Called when an interrupt arises

• Defers most I/O interrupt handling to IsrHandleInterrupt

IsrHandleInterrupt

• Handles most of the interrupts for the driver

• Upon receiving interrupts, appropriate functions are called

SendSend

• Implements the MiniportSend handler

• Handles some bureaucracy of interrupt masks and defers the actual sending to AdapCopyDown

AdapCopyDown

• Copies data from memory to the adapter

• Uses the AdapWriteUshort function to write data to the adapter from the memory buffer

AdapWriteUshort

• Writes one USHORT (unsigned short, usually 4 bytes) to the adapter

• Calls NDIS’s supplied NdisRawWritePortUshort routine

NdisRawWritePortUshort

• NDIS internal function

• Writes an USHORT value to an I/O port on the network card

Building the Driver

• Porting to MS Visual C++ Embedded workspace

• Modifying workspace settings

• Adapting parameters for Win CE compilation

Building the Driver (cont.)

• Finding suitable Project Settings

• Code Generation / Runtime settings

• Object / Library modules

• Conditional compilation settings

Building the Driver (cont.)

• Resolving compilation and linkage errors

• Modifying code for successful linkage

• Linking to the DDK

• Linking to NDIS

Results

• A lot of experience with Win CE driver development

• Internals of a WLAN driver understood and documented

• Extensive documentation written

• Working WLAN environment wasn’t set up

Reasons for failure to set up a working environment

• No support from Intel

• No hardware specification

• No external documentation for the driver

• Therefore: No practical way to debug and improve the code

Some Optimism

• The knowledge gained and documented during the project can be very helpful to future projects

• Hopefully the above mentioned resources will be available in the future

• This, together with our documentation can give future projects a very good starting point