Most designs have some asynchronous sets or resets. Uncontrollable sets/resets can lower test coverage. This video discusses how to handle asynchronous sets/resets and how to test hierarchical blocks independently even if they have a common source.
To manage asynchronous sets/resets, designers add control logic. But first, the sets/resets need to be defined at the RTL or gate-level and then evaluated through DRC checks to learn if the asynchronous sets/resets can be controlled. Sometimes, they need to be disabled during test. Tessent users can control the override of the sets/resets with test data registers via an IJTAG network.
The sets/resets need to be disabled during shift, and enabled during capture. In this video, Vidya Neerkundar describes the DFT logic that can be used to disable and enable sets/resets.
Within a chip, there may be hierarchical regions (or blocks, or cores) with asynchronous sets/resets. If they are at the boundary of a physical layout region, dedicated wrapper cells are inserted to control those sets/resets. Neerkundar describes how this core-level set/reset control aids in testing multiple cores at different times, independently of other blocks or parent levels.
If you are looking for tips on how to better handle asynchronous sets/resets to improve test coverage, we recommend watching Neerkundar’s short video.