System for sequential read of memory stream buffer detecting page mode cycles availability fetching data into a selected FIFO, and sending data without aceessing memory

摘要

A read buffering system employs a bank of FIFOs to hold sequential read data for a number of data streams being fetched by a computer. The FIFOs are located in the memory controller, so the system bus is not used in the memory accesses needed to fill the stream buffer. The buffer system stores addresses used for read requests made by a CPU, and if a next sequential address is then detected in a subsequent read request, this is designated to be a stream (i.e., sequential reads). When a stream is thus detected, data is fetched from DRAM memory for addresses following the sequential address, and this prefetched data is stored in one of the FIFOs. A FIFO is selected using a least-recently-used algorithm. When the CPU subsequently makes a read request for data in a FIFO, this data can be returned without making a memory access, and so the access time seen by the CPU is shorter. By taking advantage of page mode, access to the DRAM memory for the prefetch operations can be transparent to the CPU, resulting in substantial performance improvement if sequential accesses are frequent. One feature is appending page mode read cycles to a normal read, in order to fill the FIFO. The data is stored in the DRAMs with ECC check bits, and error detection and correction (EDC) is performed on the read data downstream of the stream buffer, so the data in the stream buffer is protected by EDC.