A 90 MHz CMOS RISC CPU designed for sustained performance

A CMOS CPU which operates at 90 MHz under typical conditions and implements an existing RISC (reduced-instruction-set-computer) 140-instruction set is described. The processor has been designed for sustained performance for workstation and both commercial and technical multiuser applications. Key performance features include a 3-ns, 32-b adder; low-skew on-chip clock buffers; and cycling off-chip caches at the operating frequency, using industry-standard synchronous static random-access memories (SRAMs). The speeds obtained are comparable to those of many emitter-coupled logic (ECL) implementations. The CPU chip includes the following hardware: integer fetch and execute unit, on-chip split I/D TLBs (translation lookaside buffers) with two-way 64 entries each, control for second-level off-chip TLBs, control for off-chip two-way split I/D writeback caches with single-bit error correction for data, full multiprocessing support hardware, inference for performance analysis and tuning, and a tightly coupled coprocessor interface.<
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