Using the Electric VLSI Design System

Chapter IX: TOOLS

| ## 6: Network Consistency Checking |

Electric is able to compare two different facets and determine whether their networks are the same. To do this, there must be exactly two windows or window partitions on the screen, and the two facets must be in these windows. Then, the Do Consistency Checking subcommand of the Network command of the Tools menu compares them, using a technique called graph isomorphism.

For an example of network consistency checking, open the library "samples.txt" and edit the facets "tool-NCCTop" and "tool-NCCBottom" (you can read the library with the Readable Dump subcommand of the Import command of the File menu). These two facets are isomorphic and the checker will find it to be so.

When you request comparison, the system displays the number of components, networks, power nets, and ground nets in each facet. Inconsistencies in these numbers generally lead to failure of comparison. Once compared successfully, components in one facet can be matched to components in the other simply by selecting one and using the Show Network subcommand.

The two networks being compared are, by default, compared only at their top levels of hierarchy. This means that facet instances are not examined, but rather are compared to equivalent instances in the other circuit. Because of this, if the two networks have different hierarchical structure, the comparison process will fail.

To overcome this situation, use the Network Options... subcommand, and check the "Hierarchical NCC" item. This instructs the comparison system to fully instantiate all facets before comparing. Comparison is then slower, but independent of hierarchical structure. Uncheck the item to restore nonflattening of the hierarchy. |

As an aid in network comparison, you can request that port names be used to help distinguish components. To do this, check "Use port names in NCC" in the above dialog. If ports have different names in the two circuits, this will option will cause comparison to fail, and should not be used.

If the two networks being compared are automorphic or otherwise difficult to distinguish, equivalence information can be specified prior to comparison. Select a component in one facet and use the Set First Equate subcommand. Then select the equivalent component in the other facet and use the Set Second Equate subcommand. Subsequent network comparisons use this information to assist the process. The list of equated components can be cleared with the Clear Equates subcommand. Note that component equivalence information is not saved in the library, and so it must be reentered if Electric is restarted.

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