Answers Database
M1.5i/2.1i: 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
Product Part: ngdbuild
Product Version: 1.5
Problem Title:
M1.5i/2.1i: Constraints: TNM's cannot be attached to tri-stated output flip flops (OFDT) via
the TIMEGRP statement.
Problem Description:
Urgency: standard
General Description:
When the TIMEGRP statement is used to tag a flip flop, the output netname of the flip flop is used t
o define the flip flop. Because of the fact that the OFDT component is actually a macro with an OFD
and a TBUF underneath, the actual output netname of the component will be unknown to the user (buri
ed beneath a level of 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 .ucf/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 - Last Modified: 07/13/99 15:18 |
