One of the challenges that processor level stimuli generators are facing is the need to generate stimuli that exercise microarchitectural mechanisms deep inside the verified processor. These scenarios require specific relations between the instructions participating in them. We present a new approach for processor-level scenario generation. The approach is based on creating an abstract constraint satisfaction problem, which captures the essence of the requested scenario. The generation of stimuli is done by interleaving between progress in the solution of the abstract CSP and generation of instructions. Compared with existing solutions of scenario generation, this approach yields improved coverage and reduced generation fail rate.

Microarchitectural information regarding various aspects of instruction execution can help processor-level stimuli generators more easily reach verification goals. While many such aspects are based on common microarchitectural concepts, their specific manifestations are highly design-specific. We propose using an automatic method for acquiring such microarchitectural knowledge and integrating it into the stimuli generator. We start by extracting microarchitectural data from simulation traces. This data is fed to a decision tree learning algorithm that produces rules for microarchitectural behavior of instructions; these rules are then integrated into the testing knowledge of the stimuli generator. This testing knowledge can provide users with the ability to better control the microarchitectural behavior of generated instructions, leading to higher quality test cases. Experimental results on the POWER7 processor showed that our proposed method can improve the microarchitectural coverage of the design.

Parallelism in processor architecture and design imposes a verification challenge as the exponential growth in the number of execution combinations becomes unwieldy. In this paper we report on the verification of a Very Large Instruction Word processor. The verification team used a sophisticated test program generator that modeled the parallel aspects as sequential constraints, and augmented the tool with manually written test templates. The system created large numbers of legal stimuli, however the quality of the tests was proved insufficient by several post silicon bugs. We analyze this experience and suggest an alternative, parallel generation technique. We show through experiments the feasibility of the new technique and its superior quality along several dimensions. We claim that the results apply to other parallel architectures and verification environments.

We report on our experience with a new test generation language for processor verification. The verification of two superscalar multiprocessors is described and we show the ease of expressing complex verification tasks. The cost and benefit are demonstrated: training takes up to six months; the simulation time required for a desired level of coverage has decreased by a factor of twenty; the number of escape bugs has been reduced.