Microsoft KB Archive/169576
PRB: OSR2 Sets Bridge Control Register ISA Enable Bit
The information in this article applies to:
- Microsoft Win32 Device Driver Kit (DDK) Windows 95
PCI devices that are assigned I/O resources by the BIOS with the lower 10 bits in the range of 100-3FFh may not work properly when installed behind a PCI bridge on Windows 95 OSR2.
OSR2 sets the PCI Bridge Control Register ISA Enable bit. Setting the ISA Enable bit causes the bridge to block I/O transactions to the device when the lower 10 bits of the address are in the range 100h-3FFh. This results in the following behavior:
I/O Range: (repeating pattern up to FFFF, only the first 10FFh bytes are shown.)
1000 - 10FF Forward D00 - FFF Block Forwarding C00 - CFF Forward 900 - BFF Block Forwarding 800 - 8FF Forward 500 - 7FF Block Forwarding 400 - 4FF Forward 100 - 3FF Block Forwarding 0 - FF Forward
This can be a problem if the BIOS assigns a PCI device I/O resources in a range that will be blocked by the ISA Enable Mode.
This problem has been resolved in the next version of the Windows operating system.
Issue type :
Technology : kbAudDeveloper kbWin95search kbWinDDKSearch kbWin32sSearch kbWin32DDK95 kbWin32DDKSearch
Last Reviewed: March 5, 1999