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Tabby CAD Suite version 20220512 released!

Formal tristate support, x handling, optimising adders.

The May release of Tabby CAD Suite is now available for download.


  • The tribuf pass now supports a -formal option that converts inferred tri-state buffers within a module into equivalent non-tri-state logic for formal verification. It automatically adds assertions that detect multiple drivers driving the same net simultaneously. (When using tri-state I/O across modules, tribuf -formal should be preceded by a flatten pass).
  • Several changes in the handling of x values during formal verification. In particular, when using the Verific frontend, during the initial time step, value change expressions ($rose, $fell, $changed, $stable) are now always computed as if the argument changed from x to its initial value. This follows the SystemVerilog standard and ensures that any high (or low) signal starts at a step where $rose (or $fell) is true.

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