UBC Theses and Dissertations
Improving the performance of post-silicon trace generation Kuan, Johnny Jone Wai
As microprocessor designs become more complex, the task of finding errors in the design becomes more difficult. Most design errors will be caught before the chip is fabricated, however, there may be some that make it into the fabricated design. The process of determining what is wrong when the fabricated chip of a new design behaves incorrectly is called post-silicon debug (also known as silicon validation). One of the challenges of post-silicon debug is the lack of observability into the state of a fabricated chip. BackSpace is a proposal for tackling the observability challenge. It does this by generating a post-silicon trace using a combination of on-chip monitoring hardware and off-chip formal analysis. To add one state to the trace, BackSpace generates a set of possible predecessor states by analysing the design which are then tested one at a time. The testing is performed by loading a candidate state into a circuit that compares it with the current state of the chip, and running the chip. If the state is reached during execution, then it is added to the trace. The process of testing states one at a time is time consuming. This thesis shows that correlation information characterizing the application running on the chip can reduce the number of runs of the chip by up to 51%. New post-silicon trace generation algorithms, BackSpace-2bp and BackSpace-3bp, are also proposed that do not need to generate the set of possible predecessor states. This leads to a speedup relative to practical implementations of BackSpace and also reduces the hardware overhead needed to generate post-silicon traces by 94.4% relative to the state of the art implementation of BackSpace. To evaluate these new algorithms BackSpace, and the new algorithms, were implemented on a superscalar out-of-order processor using the Alpha instruction set. Non-determinism was introduced in the form of variable memory latency. The effects of non-determinism on the processor and the trace generation algorithms are also evaluated.
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