Chris Cant - Writing Windows WDM Device Drivers

If you ever reboot and choose the "Original Configuration" hardware profile, you will find that the WdmIo device has been removed from the WdmIo profile. You will have to reinstall it and reboot. Sigh.

If you use WdmIo to talk to some of your own custom hardware, you will almost certainly not need to go through all of the previous shenanigans. Similarly, for a one off test of WdmIo talking to a parallel port, you should be able to install it without using different hardware profiles.

In Windows 2000 beta 2, I found that it was impossible to install a WdmIo device in place of the standard parallel port driver. If a parallel port driver was removed to make the resources available, Windows 2000 always reinstalled the driver on reboot before the WdmIo device could be loaded.

The WdmIo INF files must be set up for each device to which it will talk. A LogConfig section or sections must be added to give the resource assignments. Listing 15.5 shows the amendments that have been made to the WdmIoLpt1Checked.inf and WdmIoLpt1Free.inf installation files.

Both the Windows 98 WdmIo.Install and the Windows 2000 WdmIo.Install .NTx86 sections have a LogConfig directive that refers to the three LogConfig sections, each of which have different possible resource assignments. These eventually appear to users in the Device properties Resources tab as "Basic configuration 0", "Basic configuration 1", and "Basic configuration 2". Each section has a configuration priority. WdmIo.LogConfig1 has priority DESIRED that is higher than the NORMAL priority of the other LogConfig sections.

The WdmIo. LogConfig1 resource assignments are chosen by preference. There is only one I/O port range, 0x378 to 0x37A, so this address range is used. However, two IRQ numbers are listed, 5 and 7. Only one of these is used. In some computers, IRQ5 will already be used, so IRQ7 will be selected automatically. If both IRQs are available, the user will be prompted to make a choice.

The user, therefore, has to confirm which resource assignments to make. For the WdmIo device, Windows does not detect the parallel port and load the appropriate drivers. It is up to the device installer to select the correct resource assignments. The WdmIo driver does not care which port address or IRQ it is assigned. To do a useful job, the resources must correspond to a real device, and the controlling Win32 application must use the registers and interrupts in the correct way.

If you try to install a second WdmIo device for a parallel port, Windows should choose one of the remaining configurations. Windows 98 displays the chosen resource assignments and asks the user to confirm that these are satisfactory. It then tells you to insert the card. If the system's resource assignments have to be juggled to accommodate the new device, you may have to reboot.

Listing 15.5 WdmIoLpt1Xxx.INF LogConfig sections

[WdmIo.Install]

CopyFiles=WdmIo.Files.Driver

AddReg=WdmIo.AddReg

LogConfig=WdmlIo.LogConfig1,WdmIo.LogConfig2,WdmIo.LogConfig3

[WdmIo.LogConfig1]

ConfigPriority=DESIRED

IOConfig=378-37a

IRQConfig=7,5

[WdmIo.LogConfig2]

ConfigPriority=NORMAL

IOConfig=278-27a

IRQConfig=7,5

[WdmIo.LogConfig3]

ConfigPriority=NORMAL

IOConfig=3bc-3be

IRQConfig=7,5

[WdmIo.Install.NTx86]

CopyFiles=WdmIo.Files.Driver.NTx86

LogConfig=WdmIo.LogConfig1.WdmIo.LogConfig2,WdmIo.LogConfig3

A large number of entries can be put in Logconfig sections. For a start, further IOConfig and IRQConfig entries can be given if a device can have more than one of these resources simultaneously. The IOConfig and IRQConfig entries can be specified in a variety of ways. DMAConfig, PcCardConfig, MemConfig, and MfCardConfig entries can also be included. I found that the Windows 2000 DDK was the best source of information on all these entries.

With a WdmIo device finally installed for one of your parallel ports, it is now possible to run the WdmIoTest program. Do not forget to plug in a printer. I found that a clattery old dot matrix printer was best for testing, as it produced audible output straightaway. With a page-oriented ink jet or laser printer, you might have to press Formfeed to see the printed information.

When you run WdmIoTest, the printer should initialize itself and print out a two-line short message.

If the printer is switched off, WdmIoTest will keep checking to see if it is ready for 20 seconds. It will give up if it is not available by then. To test the time-out behavior of WriteFile, you must comment out the busy check code. If you now run WdmIoTest again, it will attempt to write information to the printer. It should time-out after 10 seconds with error 21 (ERROR_ NOT_READY).

The WdmIo driver handles the user pressing Ctrl+C correctly. I shall show in the next chapter how this IRP cancelling and cleanup occurs.

The PHDIo driver was initially aimed just at the NT and Windows 2000 platforms. However, I found that it works fine in Windows 98. These installation instructions are for both types of platform. You do not need to remove or disable existing drivers yet. Installing and running PHDIo does not make it use any resources. It only asks for resources when a Win32 program, such as PHDIoTest, runs.

These instructions describe how to install PHDIo by hand, by copying files and making registry entries. See Chapter 11 for details of how to automate this process.

Start by copying the driver executable PHDIo.sys to the Windows System32\Drivers directory. Use the checked build version of PHDIo.sys if you want to view its DebugPrint output. The version of DebugPrint supplied with this book does not run under Windows NT 3.51 or NT 4.

Make a registry key for PHDIo at HKLM\SYSTEM\CurrentControlSet\Services\PHDIo. Make the values specified in Table 15.6. The Start value of 2 indicates that the PHDIo driver should be loaded once the system is up and running. In Windows 98, also add an ImagePath REG_SZ value with \SystemRoot\System32\Drivers\PHDIo.sys.

Table 15.6 PHDIo driver registry values

Now reboot your system. The PHDIo driver should now be running. Check the DebugPrint output to see that it has generated a few start-up trace messages.

If you change the driver, the actions you must take to use the new version vary from platform to platform. In Windows 98, you must reboot the system. In NT 3.51 and NT 4, use the Control Panel Devices applet to stop the old driver and start the new one. In Windows 2000, use the book software Servicer utility to do the same job.

The PHDIo driver is started in all Hardware profiles.

The PHDIoTest software is in subdirectory PHDIo\Exe of the book software. As mentioned previously, PHDIoTest opens the PHDIo device with this filename: \\.\PHDIo\isa\io378,3\irq7\override. This filename tells PHDIo which resources to use. In this case, an I/O port of 0x0378-0x037A (length 3) and IRQ7 are specified. Change these values if your parallel port is configured differently. The \override specifier means that PHDIo should go ahead and use these resources even if they conflict with another device.