Design, implementation, and verification of active cache emulator (ACE)

This paper presents the design, implementation, and verification of the Active Cache Emulator (ACE), a novel FPGA-based emulator that models an L3 cache actively and in real-time. ACE leverages interactions with its host system to model the target system (i.e. hypothetical system under study). Unlike most existing FPGA-based cache emulators that collect only memory traces from their host system, ACE provides feedback to its host by modeling the impact of the emulated cache on the system. Specifically, delays are injected to time dilate the host system which then experiences hit/miss latencies of the emulated cache. Such active emulation expands the context of performance measurements by capturing processor performance metrics (e.g. cycle per instruction) in addition to measuring the typical cache-specific performance metrics (e.g. miss ratio).ACE is designed to interface with a front-side bus (FSB) of a typical Pentium®-based PC system. To actively emulate cache latencies, ACE utilizes the snoop stall mechanism of the FSB to inject delays to the system. At present, ACE is implemented using a Xilinx XC2V6000 FPGA running at 66MHz, the same speed as its host's FSB. Verification of ACE includes using the Cache Calibrator and RightMark Memory Analyzer software to confirm proper detection of the emulated cache by the host system, and comparing ACE results with SimpleScalar software simulations.