Answers Database

SYNERGY v4.4: Multiple source errors from XNFPREP because XNFOUT writesout OBUFT's instead of BUFT


Record #1510

Product Family:  Software

Product Line:  Cadence

Problem Title:
SYNERGY v4.4:  Multiple source errors from XNFPREP because XNFOUT
writesout OBUFT's instead of BUFT



Problem Description:
The Cadence XNFOUT tool will translate "BUFT's" into "OBUFT's" in a
Synergy VHDL or Verilog netlist whenever it does not find combinational
logic between the "BUFT's" output and the corresponding Output Pad. The
result is that you get multiple "OBUFT's" sourcing the same PAD.

While having multiple TBUFs sourcing the same signal is legal, in an LCA,
each OBUFT is connected directly to the outside world through a single
connection to an OUTPUT pad.  Thus it is illegal to try to have multiple
OBUFTs sourcing the same signal in an LCA design.

The error is flagged downstream in the XACT implementation flow when you run
XNFPREP on the design as a "multiple source" error.

This is a bug (PCR 182510) in the 9604 version of the Cadence XNFGEN utility
(XNFGEN connects pad to multiple OBUFT symbols). XNFOUT displays a similar
problem.


Solution 1:

The workaround to prevent this from happening is to instantiate OBUFs in
the VHDL or Verilog source.



End of Record #1510