Techniques for enabling in-system observation-based debug of high-level synthesis circuits on FPGAs

High-level synthesis (HLS) is a rapidly growing design methodology that allows designers to create digital circuits using a software-like specification language. HLS promises to increase the productivity of hardware designers in the face of steadily increasing circuit sizes, and broaden the availability of hardware acceleration, allowing software designers to reap the benefits of hardware implementation. One roadblock to HLS adoption is the lack of an in-system debugging infrastructure. Existing debug technologies are limited to software emulation and cannot be used to find bugs that only occur in the final operating environment. This dissertation investigates techniques for observing HLS circuits, allowing designers to debug the circuit in the context of the original source code, while it executes at-speed in the normal operating environment. This dissertation is comprised of four major contributions toward this goal. First, we develop a debugging framework that provides users with a basic software-like debug experience, including single-stepping, breakpoints and variable inspection. This is accomplished by automatically inserting specialized debug instrumentation into the user’s circuit, allowing an external debugger to observe the circuit. Debugging at-speed is made possible by recording circuit execution in on-chip memories and retrieving the data for offline analysis. The second contribution contains several techniques to optimize this data capture logic. Program analysis is performed to develop circuitry that is tailored to the user’s individual design, capturing a 127x longer execution trace than an embedded logic analyzer. The third contribution presents debugging techniques for multithreaded HLS systems. We develop a technique to observe only user-selected points in the program, allowing the designer to sacrifice complete observability in order to observe specific points over a longer period of execution. We present an algorithm to allow hardware threads to share signal-tracing resources, increasing the captured execution trace by 4x for an eight thread system. The final contribution is a metric to measure observability in HLS circuits. We use the metric to explore trade-offs introduced by recent in-system debugging techniques, and show how different approaches affect the likelihood that variable values will be available to the user, and the duration of execution that can be captured.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat