AR# 3654


A1.4/F1.4 PAR - Problems with placement of Wide Edge Decoders or associated Pullups.


The M1 mapper does a poor job of configuring a network
of Wide Edge decoders unless it is guided by edge location
constraints on all decoder symbols. The symptoms of this
problem are placement errors in PAR involving Decoders or
their associated Pullups.

Example 1.
ERROR:x4kpl:133 - Unable to resolve the placement of all
decoder groups in a legal manner. Please check decoder and
PULLUP constraints for conflicts.

Example 2.
ERROR:x4krt:3 - Pullup on signal "SKIN/MICRO/DECODES/$1N489"
is not on same edge of the die as the edge decoder. This is
required in order to route the pullup to the output of the
edge decoder; the router will terminate.


Wide Decoder Networks are handled well if the mapper
is guided by an edge constraint on each decoder symbol.

The following is an example of a .ucf file constraint that
puts a LOC constraint on a Decoder symbol:


Valid Edge constraint values: T, B, L, R
Valid half edge constraint values: TL. TR, RT, RB, BR, BL, LB, LT

Keep in mind that the decoders on a half edge must drive
a combined total of no more that four different output
AR# 3654
Date 10/21/2008
Status Archive
Type General Article
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