System and method for managing data in an i/o cache

Abstract

The present invention is generally directed to a system and method for fetching data from system memory to a device in communication with the system over a PCI bus, via an I/O cache. Broadly, the present invention may be viewed as a novel way to communicate certain fetching hints; namely, hints that specify certain qualities about the data that is to be fetched from the system memory. In operation, the I/O cache may use such hints to more effectively manage the data that passes through it. As simply one example, if, based upon the hints, the controller for the I/O cache knew (or assumed) that the data being fetched was ATM data, then it would also know (based upon the nature of ATM data) that precisely a forty-eight byte data payload was to be sent to the requesting device, and the I/O cache could pre-fetch precisely this amount of data (typically one or two cache lines). In accordance with one aspect of the invention, such a system includes an input/output (I/O) cache memory interposed between the system memory and the PCI bus, wherein the cache memory has internal memory space in the form of a plurality of data lines within the cache memory. The system further includes a plurality of registers for each PCI master that are configured to define fetching criteria. Finally, the system includes a register selector that is configured to select an active register among the plurality of registers, wherein fetching criteria for the device is specified by the active register.