Rectification of advanced microprocessors without changing routing on FPGAs (abstract only)

Abstract

We propose a method for rectification of bugs in microprocessors that are implemented on FPGAs, by only changing the configuration of LUTs, without any modification to the routing. Therefore, correcting the bugs does not require resynthesis, which can be very long for complex microprocessors due to possible timing closure problems. As the structure of the circuit is preserved, correcting the bugs does not affect the timings of the circuit. In design phase, we may add additional LUTs to the original circuit, so that we can use them in the correction phase. After a bug is found, we perform the following two tasks. Fist, we find the candidate control signals as well as the required change to correct their behavior. This is done by using symbolic simulation and equivalency checking between the formal specification and the erroneous formal model of the processor. Then, we try to map the corrected functionality into the existing LUT structure. This is done by a novel method that formulates the problem as a QBF (Quantified Boolean Formula) problem, and solves it by repeatedly applying normal SAT solvers instead of QBF solvers under a CEGAR (Counter Example Guided Abstraction Refinement) paradigm. We show effectiveness of our method by correcting bugs in two complex out-of-order superscalar processors with two different timing error recovery mechanisms.