Show description

When the design complexity doubles, it takes twice as long to complete or requires twice as many people to implement it. Neither of these situations is desirable. You need a methodology that finds bugs faster in order to reach the goal of 100% coverage. Figure 1-2 Directed test coverage Feature Test Bug Figure 1-2 shows the total design space and features that are covered by directed testcases. In this space are many features, some of which have bugs. You need to write tests that cover all the features and find the bugs.

5 Methodology Basics This book uses the following principles. z z z z z Constrained-random stimulus Functional coverage Layered testbench using transactors Common testbench for all tests Test-specific code kept separate from testbench All these principles are related. Random stimulus is crucial for exercising complex designs. A directed test finds the bugs you expect to be in the design, whereas a random test can find bugs you never anticipated. When using random stimulus, you need functional coverage to measure verification progress.

Finally, it is essential that you need to analyze the results to determine if you have met the goals, and if not, how you should modify the tests. 15 Conclusion The continuous growth in complexity of electronic designs requires a modern, systematic, and automated approach to creating testbenches. The cost of fixing a bug grows by tenfold as a project moves from each step of specification to RTL coding, gate synthesis, fabrication, and finally into the user’s hands. Directed tests only test one feature at a time and cannot create the complex stimulus and configurations that the device would be subjected to in the real world.