ACCESS: HW/SW Co-Equivalence Checking for Firmware Optimization

Customizing embedded computing platforms to specific application domains often necessitates optimizing the firmware and/or the HW/SW interface under tight resource constraints. Such optimizations frequently alter the communication between the firmware and the peripheral devices, possibly compromising functional correctness of the input/output behavior of the embedded system. This paper proposes a formal HW/SW co-equivalence checking technique for verifying correct I/O behavior of peripherals under a modified firmware. We demonstrate the great promise of our approach on RTL implementations of several open-source peripherals. In our experiments we successfully prove or disprove correctness of firmware optimizations for an industrial driver software. In addition, we also found a subtle bug in one of the peripherals and several undocumented preconditions for correct device behavior.