Low Complexity Out-of-Order Issue Logic Using Static Circuits

In this paper a single-cycle issue queue circuit architecture that simplifies the wakeup and selection logic is proposed. The micro-architecture and fully static CMOS circuits are presented for a 32-entry queue that issues four instructions per cycle. The instruction-ready signals are divided into groups and processed in parallel to issue the four oldest ready instructions. The complete issue queue and prioritization logic requires 20 inversions, allowing simulated circuit operation at over 4 GHz in a foundry 45 nm SOI fabrication process.