Answers Database

XBLOX 5.0/5.1: COUNTERs with different COUNT_TO values functionally simulate the same


Record #550

Product Family:  Software

Product Line:  FPGA Core

Problem Title:
XBLOX 5.0/5.1: COUNTERs with different COUNT_TO values functionally
simulate the same



Problem Description:
Say a design contains two or more XBLOX COUNTERs which are identical except
that each has a different COUNT_TO value.  In functional simulation (via
XSimMake or Fncsim8), these two COUNTERs count the same.

In order to save disk space, XBLOX compares similar modules to see whether
or not they can share the same simulation model.  If two modules have the
same connectivity and parameters, XBLOX uses the same model for both.  In
the case of COUNTERs, however, XBLOX 5.0/5.1 does not compare COUNT_TO
values in making this determination.  Therefore, two COUNTERs with
different COUNT_TO values can potentially simulate the same functionally.
This problem goes away when the design is placed and routed, and when it is
run through timing simulation.


Solution 1:

Change the connectivity of one of the COUNTERs slightly to make it look
different enough from the other.  For example, tie a COUNTER's unconnected
CLOCK_ENABLE high or SYNC_CTRL low.

This problem is fixed in XACT 5.2/6.0.



End of Record #550