Writing Windows WDM Device Drivers

verify that some software is licensed to run on a computer. They are designed to respond when their manufacturer's software talks to them in some special way. At all other times, they are designed to pass all parallel port signals to the printer and vice versa.

Table 15.3 Parallel port registers

Offset	Access	Register
0	Read/Write	Data
1	Read only	Status
	Bit 3	ONLINE
	Bit 5	OUT_OF_PAPER
	Bit 6	ACK#
	Bit 7	BUSY#
2	Read/Write	Control
	Bit 0	STROBE
	Bit 2	INIT#
	Bit 3	SELECT
	Bit 4	ENABLE_INT
	Bit 6	1
	Bit 7	1

WdmIoTest

The WdmIoTest application uses the WdmIo driver to write a brief message to the printer. It outputs information to the console screen to indicate its progress as it performs the following steps. Steps 2-8 all involve DeviceIoControl or WriteFile calls to the WdmIo driver.

1. Open a handle to the WdmIo device. The GetDeviceViaInterface routine is used as before to open a handle to the first device with a WDMIO_GUID device interface.

2. Disable the interrupts and connect to an interrupt.

3. Initialize the printer.

4. Send commands for writing each byte.

5. Read the status every second until the printer is ready. Time-out after 20 seconds.

6. Write a message to the printer.

7. Get the write results.

8. Disable the interrupt.

9. Close the handle.

PHDIoTest

PHDIoTest does exactly the same job as WdmIoTest, except that it obtains a handle to the PHDIo device in a different way. It calls CreateFile directly, passing the required resources in the filename, as follows.

HANDLE hPhdIo = CreateFile('\\.\PHDIo\isa\io378,3\irq7\override', GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

Table 15.4 shows the different resource specifiers that may be used as a part of the PHDIo filename. The first specifier must be isa. The other specifiers can be in any order. An I/O port specifier must be given. Use the override specifier with caution and never use it in a commercial release. All letters in the filename must be in lower case.

Table 15.4 PHDIo filename resource elements

Element	Required	Description
isa	Mandatory	Initial string: Isa bus