Method and apparatus for reducing logic activity in a microprocessor using reduced bit width slices that are enabled or disabled depending on operation width

Abstract

A method and apparatus for reducing logic activity in a microprocessor which examines every instruction before it is executed and determines in advance the minimum appropriate datapath width (in byte or half-word quantities) necessary to accurately execute the operation. Achieving this requires two major enhancements to a traditional microprocessor pipeline. First, extra logic (potentially an extra pipeline stage for determining an operation's effective bit width—the WD width detection logic) is introduced between the Decode and Execution stages. Second, the traditional Execution stage architecture (including a register file RF and the arithmetic logical unit ALU), instead of being organized as one continuous 32-bit unit, is organized as a collection of multiple slices, where a slice can be of an 8-bit (a byte) or a 16-bit (double byte) granularity. Each slice in this case can operate independently of each other slice, and includes portion of the register file, functional unit and cache memory. Concatenating a multiple number of these slices together creates a required full width processor.