Method of using stream buffer to perform operation under normal

Abstract

The operation of a stream buffer varies depending on whether a normal operation mode or a test mode is selected. In the normal operation mode, the stream buffer is read from only when the data requested by a CPU read has been determined to reside there, and the stream buffer location read from is the location determined to contain the requested data. This determination is made by comparing the address of the read request with addresses of the data stored in the stream buffer. Also, the stream buffer is written with memory data in response to a read that misses the stream buffer, and the location written to is one that has been allocated to receive the incoming memory data. Two different buffer allocation methods are shown, first-in-first-out (FIFO) and least-recently-used (LRU). During the test operation mode, the stream buffer is written to and read from directly by the CPU at locations specified in the write and read requests, without regard to the data presence determination and the allocation that take place in the normal operation mode. The method provides a straightforward way of testing the stream buffer during system operation by bypassing some normal functions during test mode in favor of direct stream buffer access by the CPU.