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AR# 1473

Foundation XVHDL: How to control the # of BUFGs which are automatically inserted.


Versions: F6.x, F1.3/F1.4

The XVHDL compiler automatically inserts BUFGs on clock
signals, according to a limit prescribed by the Foundation
Project Manager based on the target device family.

There are cases where the synthesized XNF file will contain
more BUFGs than are allowable by the target device

1. If you instantiate any Global Buffers in the design, these
will not be included in the "count".

For example, in an XC5200 design:
If you instantiate 2 BUFGs, and have 3 other clock signals
in the design, XVHDL will put BUFGs on those 3 clock
signals as well, resulting in a design using 5 BUFGs,
which is more than the number of BUFGs present in an
XC5200 device.

2. If you use the Xilinx_BUFG attribute, these BUFGs will not
be included in the "count". Same scenario as above.

So, how can you control the number of BUFGs that XVHDL
automatically inserts?


There is a command line option for XVHDL which can control this. To allow this option to be used when XVHDL is run from
the Foundation GUI, do the following:

Create a file called METAMOR.ARG in your project directory.

In this file, type the following line:
-u <n>

where <n> is the number of BUFGs that XVHDL is allowed to
automatically insert.

So, for example, in the example above where you have instantiated 2 BUFGs in an XC5200 design, you would want to
use the
-u 2
option in the Metamor.arg file.
AR# 1473
Date Created 11/06/1996
Last Updated 01/02/2000
Status Archive
Type General Article