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Instruction queues consume a significant amount of power in a high-performance processor. The wakeup logic delay is also a critical timing parameter. This paper compares a commonly used CAM-based instruction queue organization with a new pointer-based design for delay and energy efficiency. A design and pre-layout of all critical structures in 70nm technology is performed for both organizations. The pointer-based design is shown to use 10 to 15 times less power than the CAM-based design, depending on queue size, for a 4-wide issue, 5GHz processor. The results also demonstrate the importance of evaluating all steps of instruction queue access: allocation, issue and wakeup rather than wakeup alone, especially for power consumption.
Date of Conference: 2-5 Oct. 2005