Instruction Issue Policy Of Embedded Processor Based On Resource Reuse

Instruction issue policy research including three main technicals:instruction dependency check and operand forward mechanism, register renaming and the issue queue. We research on these three aspects and proposed the counter mechanism for operand forwarding, the register renaming method based on iteratively reuse the storage resource of physical register and the centralized-distributed issue queue based on the oldest the first launch.The operand forward method which based on counter mechanism uses the instruction execution cycles to determine the source operand forward time and the information of the pipeline stages to determine the forward path.In order to solve the pipeline stall caused by the physical register source conflict in deep pipeline superscalar processor, this paper present a non-blocking instruction issue method by sharing one physical register to multi-instructions. This method continues to distribute physical register even when the physical register source conflict happens by using the instruction issue queue to buffer the conflicting instructions and increasing the amount of physical registers that can be distributed. By using this method, the processor releases the issue window and improves the using parallelism of physical register. Experiments show that compared with the traditional renaming method, to achieve the same performance, iteratively reusing method saves 27.3% of the physical register resources.The centralized-distributed issue queue implements the oldest the first launch policy by using the item moving method. The oldest the first launch policy improves the instruction execution and retiring efficiency. And on the other hand, the centralized-distributed architecture improves the resource utilization of the queue but doesn't bring too much complexity to the control logic.