Method for buffering and issuing instructions for use in high-performance superscalar microprocessors

摘要

An improved method and apparatus for buffering and issuing instructions for use with superscalar microprocessors are disclosed. The method comprises the steps of: (a) obtaining an instruction buffer comprising a plurality of entries, each entry comprising a random access memory (RAM) portion and a content addressable memory (CAM) portion for storing result data and source operand tag, respectively, wherein the CAM portion also contains means for linking with an associated RAM portion and the result data contains an instruction; (b) providing a result bus capable of transmitting the result data and a result tag; (c) matching the result tag in the result bus with the source operand tag in the CAM, and writing the result data into the RAM portion of an entry if the result tag in the result bus matches the source operand tag of an associated CAM portion; and (d) issuing ready instructions and changing the source operand tag in a corresponding CAM in such a manner that the entry containing the CAM will be identified as an empty entry so as to all new instruction to be written thereto. Because instructions are stored in the RAM in an out-of-order, a linear systolic array is provided so as to keep the sequence of instructions in order. The linear systolic array, which can be easily compressed, allows the prioritization of instructions for issue among ready instructions, and the handling branch mis-prediction and faults to be implemented.