Don´t let the X-bugs bite: Conquer elusive X-propagation issues early! Get them before they get you!

Designers spend many, many hours verifying that RTL provides the correct functionality and expect that gate level simulation produces the same results as RTL simulation. However, X-propagation is a major cause of differences between gate level and RTL simulation results, and issues cannot be detected by logical equivalence checkers. While most Xs are harmless at the RTL level, they can mask functional bugs. Resolving differences between gate level and RTL simulation results is painful and time consuming because Xs make correlation between the two difficult. X-propagation issues cause costly iterations, painful debug, and sometimes allow X-related functional bugs to slip through. This invited talk explains the common sources of Xs, shows how they can mask real functional issues and why they are difficult to avoid. It also presents a unique practical solution to assist designers in catching X-propagation bugs efficiently.