Function verification approaches can be divided into two categories. Bottom-up and flat approaches.
Bottom-up approach can be done at 4 levels.
1)Unit (Module-level) Level
2)Sub-ASIC (Functional Blocks) Level
In unit level verification, a module is verified in its own test environment to prove that the logic, control, and data paths are functionally correct. The goal of module level verification is to ensure that the component/unit being tested conforms to its specifications and is ready to be integrated with other subcomponents of the product. In unit level verification good coverage percentage is expected.
In sub-asic level ,the goal is to ensure that the interfaces among the units are correct & the units work together to execute the functionality correctly. Sometimes this level can be skipped.
Asic level verification is the process of verifying the ASIC to see that it meets its specified requirements. ASIC level verification must concentrate on ensuring the use and interaction of ASIC rather than on checking the details of its implementations .
In this ,verification approaches by combining interface models and transaction streams to test the Complete ASIC.