Functional Constraint Extraction From Register Transfer Level for ATPG

The use of scan test patterns, generated at the gate level with automatic test pattern generation (ATPG) tools in design simulation, was proposed in our previous work to improve verification quality. A drawback of this method is the potential presence of illegal (or unreachable) states (ISEs) causing unwanted behavior and false error detection in the verification process. In this brief, we present a new automated tool that helps overcome this problem. The tool extracts functional constraints at the register transfer level on a VHDL description (it can be easily adapted to any other hardware description language). The constraints extracted are used in the ATPG process to generate pseudofunctional scan test patterns which avoid the ISEs. The whole verification environment incorporating the proposed tool is presented. Experimental results show the tool impact on the reduction of false error detection in verification. In addition, it shows the verification quality improvements with the proposed environment in terms of coverage, time, and complexity.