The Windows Driver Model has two separate but equally important aspects. First, the core model describes the standard structure for device drivers. Second, Microsoft provides a series of bus and class drivers for common types of devices.
The core WDM model describes how device drivers are installed and started, and how they should service user requests and interact with hardware. A WDM device driver must fit into the Plug and Play (PnP) system that lets users plug in devices that can be configured in software.
Microsoft provides a series of system drivers that have all the basic functionality needed to service many standard types of device. The first type of system driver supports different types of bus, such as the Universal Serial Bus (USB), IEEE 1394 (FireWire) and Audio port devices. Other class drivers implement standard Windows facilities such as Human Input Devices (HID) and kernel streaming. Finally, the Still Image Architecture (STI) provides a framework for handling still images, scanners, etc.
These system class drivers can make it significantly easier to write some types of device driver. For example, the USB system drivers handle all the low-level communications across this bus. A well defined interface is made available to other drivers. This makes it fairly straightforward to issue requests to the USB bus.
Conclusion
Conclusion
Please test your driver well before releasing it. You must check that your driver works on a variety of computers. It must cope with user mode program aborts.
Debugging drivers is harder than user mode applications. In the worst case, a bugcheck occurs that tells you roughly what went wrong. Resource leaks and timing problems are more difficult to sort out.
The DebugPrint software lets you insert "print" statements into your driver code. You can do source-level debugging between two computers using WinDbg, or on a single computer using the NuMega SoftICE product.
The next chapter looks at the dispatch routines in the Wdm1 device driver.
