Writing a Start I/O Routine
The remainder of this chapter discusses the development of a programmed I/O driver for a parallel port. For simplicity, this driver ignores many of the details that would have to be considered if writing a commercial driver.
Execution Context
The I/O manager calls the driver's Start I/O routine (described in Table 8.4) either when a Dispatch routine calls IoStartPacket (if the device was idle), or when some other part of the driver calls IoStartNextPacket. In either case, Start I/O runs at DISPATCH_LEVEL IRQL, so it must not do anything that causes a page fault.
What the Start I/O Routine Does
A driver's Start I/O routine is responsible for doing any function code-specific processing needed by the current IRP and ...
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