Cram: Coded Registers For Amplified Multiporting

Modern out-of-order processors require a large number of register file access ports. However, adding more ports can drastically increase the delay, power and area of the register file. This relationship imposes constraints on existing superscalar designs while impeding implementation of faster and wider out-of-order processors. In this paper, we present a novel multi-ported register file using concepts from network coding. We split a true multi-ported register file into two interleaved banks, each having half the read and write ports. A third bank, storing the XOR of the write backs to the other two banks, is added to amplify the read and write bandwidth. When compared to a conventional register file, our 8R4W 128-entry coded CRAM register file reduces leakage power by 48%, area by 29% and delay by 9%. In addition, for SPEC2006 benchmarks, our implementation consumes 40% less register file dynamic energy on average with IPC degradation of 3%.