VIS-F: Front End

VIS-F is the front end. It provides an in-memory representation of BLIF-MV. This hierarchical representation can be traversed and manipulated. VIS-F consists of the following packages:

• vm - Contains the main() function, and provides the compilation date, version number, and the location of the VIS library.¹
• cmd - The interactive command interface. Provides a global table to store values for user-settable variables (e.g., the value autoexec ). Also provides the system level commands like help , alias , and set.²
• mvf - A data structure to represent multi-valued input, multi-valued output functions, based on BDDs.
• tbl - A data structure to represent multi-valued relations, in particular the .table construct in BLIF-MV.
• var - A data structure to represent multi-valued variables, in particular the .mv construct in BLIF-MV.
• hrc - Data structures to represent a hierarchical design, in particular the .model, .subckt, and .latch constructs in BLIF-MV.
• io - Routines to read and write BLIF-MV and BLIF files.
• tst - A package template that can be used as the starting point for the creation of new packages.

When a BLIF-MV file is parsed, a directed acyclic graph of models is created by the io package, corresponding to the hierarchy given in the file. The DAG is then transformed by io into a tree by creating separate nodes for each instantiation of a model. Traversal and manipulation of the hierarchy takes place on the tree, and not the DAG, using routines provided by hrc.

The Hrc_Node_t data structure provides a lookup table for applications (e.g., VIS-V and VIS-S) to store data associated with a node in the hierarchy. In this manner, VIS-F can remain independent of VIS-V and VIS-S.