Masking IRQ's for PCMCIA Devices

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

SYMPTOMS

You may receive the following error message in the system log of Event Viewer when you use a PC Card:

   Event ID: 7000
   Source:  Service Control Manager
   Description:  A device attached to the system is not functioning

CAUSE

This problem occurs when the PC Card attempts to use an IRQ that is already in use.

RESOLUTION

Windows NT does not provide a user interface to set a PC Card to a specific IRQ. Therefore, you must edit the registry to resolve this problem.

NOTE: For these steps to work, you must already have Windows NT installed on the computer that has the PC Card connected to it.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

Use Registry Editor to perform the following steps:

1. Start Registry Editor (Regedt32.exe), and go to the following subkey:

         HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Pcmcia.
   

2. On the Edit menu, click Add Value.

3. Add the following values:

         Value Name:  InterruptMask
         Data Type:   REG_DWORD
         Data:        see note below
         RADIX:       HEX
   
      NOTE: The Data field will actually be a four digit hexadecimal number.
      To determine the value of the data field you must know which IRQ's you
      are trying to mask or hide. You must also know what the valid IRQ's are
      for this card. You can use the Pcmcmd.exe command from the
      Support\Debug\i386 directory on the Windows NT 4.0 CD. Look for the IRQ
      Level Mask to get the valid IRQ's for the card.
   
      Each IRQ is represented by it's associated binary place holder 0 - 15.
      Each of the four hexadecimal numbers in the Data field represent 4
      binary digits of the Interrupt Mask. So if we had a PCMCIA card that
      could take IRQ 11, 10, 9, 7, 5, and 3, the default InterruptMask would
      be f157. Also, if you wanted to mask IRQ 5, you would set the 5th digit
      to 1 which could be achieved with a DATA value of f177. This would look
      similar to the following table:
   
   
      IRQ's:  15 14 13 12   11 10  9  8    7  6  5  4    3  2  1  0
      VALUE:   1  1  1  1    0  0  0  1    0  1  1  1    0  1  1  1 = f177
   
      A value of 1 in the mask makes the IRQ unavailable. A value of 0 leaves
      it available. With the preceding example, the f of f177 masks IRQ's 12-
      15, the 1 of f177 leaves IRQ 9, 10, 11, but masks 8. The middle 7 of
      f177 mask IRQ 4-6 and leaves 7 available, and the last 7 of f177 mask 0-
      2 and leaves 3 available.
   
   

4. Click OK, and then exit Regedt32.

5. Restart the computer and the PC Card should no longer select IRQ 5.