Overview

Let's finally talk to some real hardware. The next chapters discuss the WdmIo and PHDIo drivers. These general-purpose drivers give Win32 programmers access to simple hardware devices. You can do basic reads and writes of hardware ports. The drivers also let you perform interrupt driven I/O. There is just enough functionality to let a user mode application send output to a standard LPT printer port. Although this is not the recommended way to talk to a printer port ^[1], it does show that these drivers can be used in a real application.

The generic nature of the WdmIo and PHDIo drivers does make them slightly more complicated to understand. However, a complete and genuinely useful driver is worth having. Using a generic driver as an example also shows all the steps that a you need to use it as the basis of a more advanced driver.

To make these drivers easier to understand, this chapter looks at the interface they make available to Win32 programmers. I will use the test programs WdmIoTest and PHDIoTest, which send a test message out a parallel port to a printer, as an example. This chapter also looks at the installation and resource allocation issues for these drivers.

The following chapters explain how the WdmIo and PHDIo drivers work. They explain the following topics in detail.

• Queuing IRPs for serial hardware I/O

• StartIo routines

• Cancel routines for queued IRPs

• Handling the Cleanup IRP

• Interrupt...