Answers Database

M1.5 Constraints: TNM's cannot be attached to tri-stated output flip flops (OFDT) via the TIMEGRP statement.


Record #800

Product Family:  Software

Product Line:  FPGA Implementation

Problem Title:
M1.5 Constraints: TNM's cannot be attached to tri-stated output flip
flops (OFDT) via the TIMEGRP statement.



Problem Description:
Keywords: OFDT, OFD

Urgency: standard


When the TIMEGRP statement is used to tag a flip flop, the output netname of the
 flip flop is used to define the flip flop.  Because of the fact that the OFDT c
omponent is actually a macro with an OFD and a TBUF underneath, the actual outpu
t netname of the component will be unknown to the user (buried beneath a level o
f hierarchy).  Because the output netname will be unknown, the flip flop will no
t be included in the timegroup.

This occurs no matter where you define the TIMEGRP: on the schematic or in a .uc
f/cst file.



Solution 1:

Use the TNM parameter to manually tag the OFDT components.
Within the UCF file try:

INST my_ofdt_instance_name1234 TNM = abc;

After the TNM's have been applied, the TIMEGRP statements
will then be valid. Of course, if there is a unique net
going to the OFDTs that you want to place in the Timegroup,
you can still place a TNM on a net (such as clock net or
enable net) and let the forward tracing mechanism group the
OFDTs.




End of Record #800