Pinpointing Interrupts in Embedded Real-Time Systemsusing Context Checksums

When trying to track down bugs using cyclic debugging, the ability to correctly reproduce executions is imperative. In sequential, deterministic, non-real-time software, this re-producibility is inherent. However, when the execution is affected by preemptive interrupts, this will have severe ef-fects on the ability to reproduce program behaviors deter-ministically, since a reproduction requires the interrupts to hit the program at the exact same instructions. In previ-ous methods, this problem has been solved using different kinds of instruction counters, that induce large execution time perturbations, demand for specialized hardware, or provide inexact results. This makes them highly unfit for resource-constrained embedded real-time systems. In this paper, we propose an alternative method for pin-pointing interrupts in embedded real-time systems using context checksums, which is not dependent on specific hard-ware features or special compilers- but which rather can be applied to any system. Although context checksums in some cases also prove inexact or ambiguous, we will show that they serve as a practical method for pinpointing and reproducing interrupts in embedded real-time systems. Fur-thermore, our method performs perfectly well with standard development tools and operating systems, requires no addi-tional hardware support and, according to preliminary re-sults, consumes merely a tenth of the execution time of ex-isting software-based methods for pinpointing interrupts.