Performance enhancement scheme for a risc type vlsi processor using dual

Abstract

Performance of a VLSI processor of the reduced instruction set computer (RISC) type is enhanced by executing two instructions simultaneously in the two execution units of the processor. There is very little increase in the cost of hardware. Three embodiments are presented with different cost and performance capabilities. The first embodiment has an instruction input to an instruction buffer (10) and two sets of control ROSs (40 and 42) and control registers (64 and 65). The control ROS and control register which is chosen depends on which instruction execution unit is to execute the instruction. Data inputs to the execution units is from a register file (48) which has an additional pair of outputs (51) and (53) that provide the data paths for simultaneous execution of instructions by the execution units. Execution unit I has an arithmetic and logic unit (ALU) (24), while execution unit II has a rotate (26) and mask generator (31). Load balancing between the two execution units can be performed by adding a multiplier (60) and divider (62) to execution unit II. In the second embodiment, additionally, load balancing is achieved by incorporating an adder (78) into execution unit II. The adder (78) is used to perform address calculations to speed up the load, store and branch instructions. In the third embodiment, an additional ALU (90) is added to execution unit II to allow the instruction processing to be further balanced between the two execution units.