Fast specification of cycle-accurate processor models

Abstract

This paper introduces a new specification style for processor microarchitectures. Our goal is to produce very simple, compact, but cycle-accurate descriptions, in order to enable early exploration of different microarchitectures and their performance. The key idea behind our approach is that we can derive the difficult-to-design forwarding and stall logic completely automatically. We have implemented a specification language for pipelined processors, along with an automatic translator that creates cycle-accurate software simulators from the specifications. We have specified a pipelined MIPS integer core in our language. The entire specification is less than 300 lines long and implements all user mode instructions except for coprocessor support. The resulting, automatically-generated, cycle-accurate simulator achieves over 240,000 instructions per second simulating MIPS machine code. This performance is within an order of magnitude of large, hand-crafted, cycle-accurate simulators, but our specification is far easier to create, read, and modify.