RISC microprocessor architecture implementing multiple register sets

Abstract

A register system for a data processor which operates in a plurality of modes. The register system provides multiple, identical banks of register sets, the data processor controlling access such that instructions and processes need not specify any given bank. An integer register set includes first (RA[23:0]) and second (RA[31:24]) subsets, and a shadow subset (RT[31:24]). While the data processor is in a first mode, instructions access the first and second subsets. While the data processor is in a second mode, instructions may access the first subset, but any attempts to access the second subset are re-routed to the shadow subset instead, transparently to the instructions, allowing system routines to seemingly use the second subset without having to save and restore data which user routines have written to the second subset. A re-typable register set provides integer width data and floating point width data in response to integer instructions and floating point instructions, respectively. Boolean comparison instructions specify particular integer or floating point registers for source data to be compared, and specify a particular Boolean register for the result, so there are no dedicated, fixed-location status flags. Boolean combinational instructions combine specified Boolean registers, for performing complex Boolean comparisons without intervening conditional branch instructions, to minimize pipeline disruption.

What is claimed is:  
     
         1 . An apparatus executing a set of instructions, the instructions including one or more fields, wherein a field of a given instruction specifies a source of an operand of the given instruction or a destination of a result of the given instruction, and wherein the apparatus comprises: 
 processing means for executing the instructions; and    a register file, coupled to the processing means, for storing operands and results of the instructions, wherein,    the register file includes a plurality of register sets, and    the register file is responsive to one or more of the fields in a given instruction to retrieve an operand of the given instruction from, or store a result of the given instruction into, a given register in a given one of the register sets as identified by the one or more fields in the given instruction.