Answers Database

SYNOPSYS: XNFPREP issues ERROR 3673 due to multiple clock buffers inserted.


Record #438

Product Family:  Software

Product Line:  Synopsys

Problem Title:
SYNOPSYS: XNFPREP issues ERROR 3673 due to multiple clock buffers
inserted.



Problem Description:
The FPGA Compiler and the Design Compiler are capable of automatically inserting

global buffers (BUFG) on clock nets and high fan-out nets. However, the problem

lies in the number of global buffers that get inserted. The compiler may insert
more
global buffers than are available on the device. This causes XNFPREP to terminat
e
with an error message.


Solution 1:

To avoid the excessive use of global buffers on clock nets, explicitly define wh
ich ports
are clock ports. Do this by declaring that all ports are "not clock" ports; and
then defining
which ports are indeed clock ports.

In a script file or on the command line, type:

set_pad_type -no_clock all_inputs()
set_pad_type -clock {clk1,clk2,sig1}

where clk1, clk2 and sig1 are the clock nets used in this example. Replace these
 signal
names with the actual names in your design.

You might get the following warning from Synopsys:

Warning: I/O pad attribute mismatch on port 'generic_input' (OPT-1014)

This is not a problem. An IBUF will be used for the non-clock ports.






End of Record #438