Answers Database
Virtex designs running ngdbuild: ERROR:NgdHelpers:342 - input pad net "xxxx" drives multiple buffers
Record #6034
Product Family: Software
Product Line: FPGA Implementation
Product Part: ngdbuild
Product Version: 1.5is2
Problem Title:
Virtex designs running ngdbuild: ERROR:NgdHelpers:342 - input pad net "xxxx" drives multiple
buffers
Problem Description:
Urgency: Standard
Problem description:
For schematic based virtex designs, if an IPAD drives both the IFD or ILD and
IBUFcomponents, the following error message will come up during ngdbuild:
ERROR:NgdHelpers:342 - input pad net "xxxx" drives multiple buffers
This same connection will work in 4K families.
Solution 1:
The convention for directing Flip Flops and Latches into IOBs have changed
in Virtex. Users should use explict IBUF and FD or LD components with
IOB=true attribute.
The reason why the above connection fails in ngdbuild is because the
underlying schematics for IFD or ILD consists of an IBUF and a FD or
LD cell, and one IPAD can't drive 2 IBUFs at the same time.
Using the following connection will workaround this problem.
IPAD signal connects with one IBUF. Then the output of the IBUF connects
to the rest of the logic in the design, and connects to a FD or a LD
component. Put IOB=true attribute on them or in the ucf file.
This connection is equavalent to an IPAD connecting to an IBUF and an
IFD or ILD.
End of Record #6034 - Last Modified: 03/29/99 12:10 |
