A 2.1GHz 6.5mW 64-bit Unified PopCount/BitScan Datapath Unit for 65nm High-Performance Microprocessor Execution Cores

  • Authors:
  • Rajaraman Ramanarayanan;Sanu Mathew;Vasantha Erraguntla;Ram Krishnamurthy;Shay Gueron

  • Affiliations:
  • -;-;-;-;-

  • Venue:
  • VLSID '08 Proceedings of the 21st International Conference on VLSI Design
  • Year:
  • 2008

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Abstract

This paper describes a unified PopCount/ BitScanForward/BitScanReverse datapath circuit designed for 2.1GHz operation with total power consumption of 6.5mW, targeted for 65nm 64-bit microprocessor execution cores. The unified datapath uses a hybrid 3:2 compressor-based Wallace tree to count the number of `1's in the 64-bit input, along with a novel encoding scheme that enables reuse of the same tree to identify the bit-location of the 1st set bit when scanning the input in the forward and reverse directions. This circuit thus combines the functions of 3 separate units, enabling 26% reduction in total energy and 20% lower area, while achieving single-cycle latency & throughput.