Answers Database
2.1i Ngdbuild- ngdbuild ignoring drive strength constraints attached to output nets
Record #7071
Product Family: Software
Product Line: M1 Implementation
Product Part: Constraints Editor
Product Version: 2.1i
Problem Title:
2.1i Ngdbuild- ngdbuild ignoring drive strength constraints attached to output nets
Problem Description:
urgency: standard
problem description: when the constraints editor is used
to create a drive strength constraint for an output port, the
constraint is ignored by the implementation tools.
Solution 1:
The constraint produced for the drive strength is similar to the following :
NET "c<0>" Drive=2;
This is a correct drive strength format. However, M2.1i ngdbuild ignores
this attibute when it is attached to the net.
The workaround is to attach the
constraint to an IOB component such as an OPAD or OBUF.
If using schematic, attach to constraint directly to the
OPAD or OBUF component.
If using synthesis, use the synthesis engine's attributes or synthesis
constraints editor. Alternately, you can use the netlist to determine
the component names, in most cases the names produced are
predictiable from synthesis run to synth run, and use the UCF file.
UCF example:
INST "c_obuf<0>" Drive=2;
where c_obuf refers to the output buffer for that IOB.
This problem is fixed in the latest 2.1i Service Pack available at:
http://support.xilinx.com/support/techsup/sw_updates/
Solution 2:
Another workaround is to instantiate OBUF_S_<current drive> or put it in the schematics
End of Record #7071 - Last Modified: 10/15/99 14:34 |
