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AR# 7733

3.1i Virtex MAP - Error: "...Unable to pack the register xxx because of connectivity restrictions."


Keywords: connectivity restrictions, xvkpu, FDRS

Urgency: Standard

General Description:
MAP fails to pack two FDRSs with common set/reset nets. (The same pack worked in version 1.5i.)

ERROR:xvkpu - Unable to obey design constraints (MACRONAME = U1/hset, RLOC = R6C0.S1) which require the combination of the following symbols into a single slice:

FLOP symbol "U1/$I887" (Output Signal = &__A__16)
FLOP symbol "U1/$I888" (Output Signal = &__A__15)
LUT symbol "U1/$I902" (Output Signal = U1/I2)
MUXCY symbol "U1/$I743" (Output Signal = U1/$I743/O)
MUXCY symbol "U1/$I858" (Output Signal = U1/$I858/O)
LUT symbol "U1/$I796" (Output Signal = U1/I3)
Unable to pack the register U1/$I888 because of connectivity restrictions.


The problem is that both flip-flops were driven by non-RLOC'd XORCY components. When combined with the fact that the FFs are using both set and reset, this led MAP to incorrectly assume that there was a conflict over the BY input pin.

The work-around is to add .ucf file constraints to RLOC the XORCYs:

INST "U1/$I853" RLOC = "R6C0.S1" ;
INST "U1/$I724" RLOC = "R6C0.S1" ;

This problem is fixed in software version 4.1i.
AR# 7733
Date 06/13/2002
Status Archive
Type General Article