This features allows two new instructions in the tech file "drc"
section: "exception <name>|none" and "exemption <name>|none". The
purpose of these rules is to allow DRC rule exceptions for certain
areas which are marked, usually by a GDS identifier layer. Because
GDS identifier layers can be cast as "mask-hint" properties, the
DRC rule exceptions make use of that (recent) feature. So rules
can be specified as "exceptions" (rule applies for layout inside
the marked area) or "exemptions" (rule is ignored for layout inside
the marked area). Rules following the statements will have the
exception or exemption applied until another exception or exemption
statement is given. Either "exception none" or "exemption none" will
stop applying any rule exception or exemption. This is especially
useful for applications like SRAM where there may be a number of
rule exceptions on different layers. The previous way to handle
that was to create new layers in magic for any layer that needed a
rule exception. That mainly resulted in very messy tech files,
and a large number of defined layers. This implementation is both
simpler and cleaner.
area + halo but then failing to limit overlap checks to that clip
area, resulting in bizarre errors whenever an array is made. Not
sure why the error didn't show up more often.
the handling of subcell instances generally. Previously it would check
the interaction between neighboring cells in an array without regard to
any material in the parent cell which might remove those errors;
consequently, the array would have to be DRC clean by itself in order for
the parent cell to show as DRC clean. The array check has been moved
inside the DRCInteractionCheck() routine, so that it runs only where
arrayed instances do not interact with anything else. Within interaction
areas, the area is flattened and checked, so the array check is not
needed.
DRC records contain an index into a string array instead of containing
a copy of a string. This is preliminary to changing the way the DRC
error plane is painted, so that the types painted will mark the error
type. This will (1) allow "drc why" to simply scan the DRC error
plane rather than running the DRC engine, (2) allow DRC errors to be
counted by area rather than by tile, and (3) let the DRC count be the
same whether done by "drc listall why" or "drc count".
R. Timothy Edwards
Darryl L. Miles