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AR# 22644

8.1i NetGen, Timing Simulation Virtex-4 - Verilog X_IDELAY model does not have a tap delay of 75ps when used in 'fixed' mode

Description

Keywords: simulate, SimPrim, idelay, x_idelay, delay

According to the Virtex-4 User Guide, each tap of an IDELAY should shift the output by 75ps. The VHDL SimPrim model appears to do this, but the Verilog one does not. Why is this?

Solution

This is a known issue with the way in which NetGen is writing out the netlist.

This issue is fixed in ISE 8.1i Service Pack 2.

There is a patch available for ISE 8.1i Service Pack 1 for this issue:
http://www.xilinx.com/txpatches/pub/swhelp/ise8_updates/cr218903.tar.gz

The instructions on using the patch is below:

Date: 9th January 2006

File Name: cr218903.tar.gz

Description: Patch for CR218903. NetGen does not buffer the input to the X_IDELAY primitive.

Platform: All

Applicable Software version: ISE 8.1i Service Pack 1

Installation/Use:

Extract the archived file as shown below:

PC :

Use any unzip utility to unarchive this file.

Once the file is unarchived, the following directory should be visible:
virtex4

Set an environment variable called MYXILINX to point to this directory.

For example, if the directory is in the "C:\cr218903" folder, the environment variable would be set as follows

> set MYXILINX=C:\cr218903

Setting MYXILINX will override the XILINX variable when using the data files.

Unix / Linux:

Type the following:
>gunzip cr218903.tar.gz
>tar -xvf cr218903.tar

Once the file is unarchived, the following directory should be visible:
virtex4

Set an environment variable called MYXILINX to point to this directory.

For example, if the two directories are in the "/home/duthv/CR218903"
folder, then the environment variable would be set as follows:

> setenv MYXILINX /home/duthv/CR218903

Setting MYXILINX will override the XILINX variable when using the data files.

Testing:

Once the files are extracted and the MYXILINX environment variable is set, please retry NetGen and the HDL file should be generated accurately.

If it does not work, verify that the MYXILINX variable does point to the directory where the "virtex4" directory resides.

This can be done by typing the following:

PC :

echo %MYXILINX% in a command prompt window

Unix / Linux :

echo $MYXILINX in a terminal/xterm window.
AR# 22644
Date Created 09/04/2007
Last Updated 11/17/2008
Status Archive
Type General Article