Cisco Technology, Inc.

Kuan-Yuh Ko

Eric Trehus

A transfer type selector selects a transfer type used for maintaining cache coherency according to address values used for accessing memory and is programmable so that different transfer types can be selected for different applications. In one embodiment, a table has different address ranges each having associated transfer types. Transfer type selection logic selects one of the transfer types associated with the address range containing the address in a memory transaction request.

Method and apparatus for selecting transfer types

Address based prefetch logic varies prefetching according to address values in read requests. The address based prefetch logic can vary how much data is initially read into a prefetch buffer or when a prefetch buffer is refilled to an initial prefetch amount. One advantage of the address based prefetch logic is that prefetching and prefetch buffer refill rates are tuned for particular application. This is important since the system controller ordinarily does not know how much data the master is requesting beyond the first data phase. The requested read address is used as a hint to determine how much prefetching needs to occur. Over prefetching wastes memory bandwidth, and potentially adds latency to other masters sharing common busses. Under prefetching may cause the system controller that is acting as a PCI target to terminate the master's read request, thus wasting PCI bandwidth, adding latency.

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San Jose, CA, United States of America

Kuan-Yuh Ko