Microsoft KB Archive/238871

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PCI Resource Conflicts When You Resume from Suspend Mode

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Q238871

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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

Keywords : kbenv

Issue type : kbinfo

Technology : kbWin95search kbWin95