Techniques for Functional Test Pattern Execution

Functional debugging of application specific integrated circuits (ASICs) has been recognized as a very labor-intensive and expensive process. It often dominates the time and cost of the ASIC system development. The difficulty of functional debugging is mainly due to the limited controllability and observability of the storage elements in designs, and therefore the intermediate variables in functional specifications. Debugging process can be logically divided into five phases: functional test generation, functional test execution, error detection, error diagnosis, and error correction. We propose a new approach for the functional test pattern execution phase. The goal is to maximize the simultaneous controllability of an arbitrary set of the user selected variables in the design at the debugging time for facilitating the functional test pattern execution while minimizing the hardware overhead. The new approach is based on the divide and conquer optimization paradigm. Functional specification of the design is logically partitioned into linear and nonlinear components. The full controllability of each component is achieved by exploiting resource sharing of a set of variables in the components and primary inputs. The most important property of the selected variables is that they enable direct and complete answers on all possible questions related to simultaneous controllability of an arbitrary set of variables in the design. The selection of the variables introduces an interesting combinatorial optimization problem. We establish its computational complexity and propose a non-greedy heuristic algorithm. The approach imposes minimal restriction on register sharing so that the synthesized designs will have the desired characteristic while minimizing the additional hardware overhead and minimizing the disruption of the optimization potential when scheduling, allocation and binding tasks in high-level synthesis are performed. The effectiveness of the proposed approach is demonstrated on a number of designs.