PCI Device Using Prefetchable Memory Generates Code 15

• Microsoft Windows 95 OEM Service Release versions 2, 2.1

SYMPTOMS

When you have a PCI device installed behind a PCI-to-PCI bridge, it may be listed in Device Manager with an exclamation point in a yellow circle. The status for the device on the General tab may report Code 15, indicating a resource conflict.

CAUSE

The computer's BIOS may not support the memory addressing needed to use the device in its current slot. For some PCI slots, BIOS support for Prefetchable Memory Addressing is required.

RESOLUTION

Contact the computer's manufacturer to obtain a BIOS update that supports Prefetchable Memory Addressing for devices on the PCI-to-PCI bridge.

You may also be able to resolve the problem by moving the peripheral device to a slot that is not behind a PCI-to-PCI bridge.

MORE INFORMATION

Prefetching addresses the problem of increasing memory latency relative to the CPU core speed. Beyond data caching, data prefetching is an effective way to address the memory access bottleneck associated with high- performance processors. This is particularly true for programs whose working sets cannot be easily fit into the on-chip data cache (the L1 cache).

The prefetching cache uses a technique for hiding memory latency by exploiting the overlap of processor computations with data accesses. A prefetching cache generates prefetch requests to bring data into the cache before it is actually needed, allowing overlap with pre-miss computations.

The prefetchable memory is speculative. However, devices that are designed to take advantage of prefetching can increase performance by reducing misses. A device that supports prefetchable memory marks data with a bit as either suitable or unsafe for prefetching. A BIOS not written to take advantage of this feature may experience problems with the configuration of the device.