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AR# 5889

1.5i Virtex Map - MAP is dropping some FF paths from Period constraint.


Keywords : map, pcf, ffs, missing, worst case, timing, errors, period, constraints

Urgency: Standard

Problem Description:
On Virtex design Worst case paths are not always covered by the PERIOD constraint.



MAP is dropping some FFS from the timing groups. Hence under
timing analysis worst case path is not always shown.

A work around is to use a FFS to FFS constraint instead.

This problem is fixed for the 2.1i release scheduled to be released
in June, 1999.


Do custom timing analysis in the Timing Analyser to cover the FFs to FFs path.


The missing paths may not just be FF to FF but can also
be from FFs to BlockRams. So the period timespec has to be
replaced by 4:
From:To's - FF->FF, FF->Ram, Ram->FF,
Ram->Ram. Although this can be
reduced to 1 timespec with some use of time groups.

Also the period spec always has lower priority than
from:to so when you replace it you need to start using explicit
PRIORITY values to preserve multicycle from:to definitions.

In 1.5i the priority scheme is: tig, from:to, and period.
In 2.1i the priority scheme is: tig, from:thru:to, from:to, offset, and then period.


Add the missing entries to the PCF file time groups so that these paths are considered by PAR.
AR# 5889
Date 04/25/2000
Status Archive
Type General Article