Overview

Before looking at other aspects of WDM drivers, it is worth while looking at how to test and debug drivers. This chapter explains how to use the DebugPrint tool that comes with the book software. This lets a driver "print" debug event messages to a Win32 application, the DebugPrint Monitor.

A later chapter looks in detail at how the DebugPrint software works.

Keep your driver as simple as possible to make it easier to test and debug.

Oh, and needless to say but I will say it anyway comment your driver very well. Document it well. Do not forget to update your comments and documentation as the driver develops.

Test, Test, Test

Developers usually want to start debugging only when they suspect something has gone wrong with their software. However, it is especially important to start work early with device drivers. Even if you think a driver is doing its job, check it thoroughly. Do not get a first cut working and ship it to customers immediately.

Here is an example of a situation where I did not test code properly. When developing the DebugPrint software, I needed to implement a formatted print function. I could not use sprintf, as this function might use facilities that are not available to kernel mode drivers.

To make things simple, I developed the routines in a Win32 program and got them working. I copied the source over to the DebugPrint driver. A quick test seemed to indicate that...