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Q238871: PCI Resource Conflicts When You Resume from Suspend Mode

Article: Q238871
Product(s): Microsoft Windows 95.x Retail Product
Version(s): WINDOWS:95
Operating System(s): 
Keyword(s): kbenv
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft Windows 95 
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SUMMARY
=======

On Windows 95 Service Release 2 (OSR 2, 2.1, and 2.5), after a computer
suspends, and then resumes, PCI devices with option ROM, that are installed
behind a PCI to PCI bridge, may show a resource conflict (code 12) in Device
Manager.

MORE INFORMATION
================

During POST (Power On Self Test), when the BIOS assigns resources to a device,
it does not allocate a memory window for the option ROM; but it does allocate
memory windows, as requested in the device's configuration space, and maps them
to high memory (above the top of system RAM).

When the computer resumes after being in Suspend mode, Windows 95 reenumerates
the PCI devices, and reallocates the memory windows (as the BIOS did during
POST). Windows also allocates an additional memory window for access to the
option ROM.

Windows 95 cannot allocate any memory windows for the device below 1MB; because
the PCI bridge memory aperture "cannot be" programmed to access low memory. The
option ROM window must be below 1MB in order to work correctly, and the result
is a resource conflict for the memory window.

Unlike Microsoft Windows 98, Microsoft Windows 95 does not support the necessary
PCI to PCI bridging functionality. It is possible to overcome this problem by
checking "Override Bridges" in the PCI bus properties of Device Manager. This
causes Windows 95 to override the PCI bridge settings and reprogram the bridge
to accommodate the additional memory window mapped below 1MB. If this is done,
other boot devices behind the PCI to PCI bridge (such as SCSI drives) may fail,
if their option ROM cannot accommodate Windows 95 reprogramming the PCI bridge.


Additional query words: pci resume resource conflict

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Keywords          : kbenv 
Technology        : kbWin95search kbZNotKeyword3
Version           : WINDOWS:95
Issue type        : kbinfo

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