A 4R2W register file for a 2.3GHz wire-speed POWER™ processor with double-pumped write operation

In multi-ported register files, memory cell size grows quadratically with the total number of ports due to wordline and bitline wiring. Reducing the number of physical access ports in a memory cell can thus lead to significant area and power savings as well as latency improvement. Double-pumped register files operate access ports twice in a single clock period to reduce area by halving the number of physical ports in the memory cell-a technique often confined to low-frequency applications. Replication of a memory cell in separate arrays halves the number of physical read ports in each copy. In this work, double-pumped write ports and replicated read ports are applied to a 4R2W register file in a high performance microprocessor product. This paper describes detailed implementation and measured hardware characteristics of this array and demonstrates a fast error correction scheme. The techniques used balance high efficiency and low latency and thus differ from previous work, in which double pumped ports perform a write followed by a read in a very large register file or where write ports are double-pumped without cell-level read port reduction.