Writing Windows WDM Device Drivers

49

Note that there are two uses of the word 'class'. Device drivers use the Windows USB class drivers to get access to the USB system. Each USB device can be categorized as a basic USB device, or as belonging to a class of USB devices such as HID, printer, etc.

50

The Windows 2000 DDK defines the Interface power descriptor structure. However, it is not apparent whether this information is used by the system USB class drivers.

51

Presumably to avoid unnecessary copying of large buffers.

52

Unlike a processor execution stack, there is nothing wrong with altering the next item down the stack.

53

The UsbGetIdleRate routine shows how to read the idle rate. 

54

 Note that the call to UsbBuildInterruptOrBulkTransferRequest must be in the loop for it to work in W2000. 

55

Using KeQuerySystemTime is less efficient. 

56

In Windows 98, I found that I could not type on my HID keyboard after a reboot.

57

This is called Draft#4 compliance. An older Draft#3-compliant device returns the HID descriptor after the endpoint descriptors.

58

Kernel mode HID clients can get and set the ring buffer size using two IOCTLs.

59

The device to which you are connecting must accept a Create IRP call with an empty filename.

60

So far, we have not considered how the kernel calls our driver. However, to be most efficient, we should not block while processing an IRP for very long. Blocking in a Power or PnP IRP handler or a system thread is fine.