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AR# 12326

4.1i Virtex-II BitGen - A patch is available to correct Virtex-II bitstream generation. Does it affect bitstream size?


Urgency: Hot

General Description:

A patch is available to correct Virtex-II bitstream generation. This patch MUST BE installed onto the 4.1i software, and it applies to all Virtex-II devices -- there are no exceptions to this requirement.

All bitstreams generated prior to this patch must be regenerated. To ensure that the correct bitstream is used, match the value of the "Bits:" field in the ".rbt" file to the Bitstream Size table below.

This problem is fixed in the latest 4.1i Service Pack, available at:

The first service pack containing the fix is 4.1i Service Pack 2.

(You will see a slightly different bitstream size when using the patch versus 4.1i Service Pack 2. The patch will create a bitstream that is 64 bits larger than 4.1i Service Pack 2. Both bitstreams are functionally equivalent.)

The bitstream sizes are as follows:

Bitstream Size
Bitstream Size

NOTE: 17V01, 17V02, and 17V04 PROMs do not support parallel configuration. Because of this, you might need to use 17V08 or 17V16 PROMs if you are configuring via SelectMap mode.


BitGen Patch

The patch can be downloaded from the following locations:

For Windows NT/98:


For Solaris:


For HP:


Set the following environment variable after installing the patch:

PC Platform:


(This should be done at the MS-DOS command prompt, or via the Control Panel -> System menu tabs.)

UNIX Workstation:


This environment variable must be set even if you are using a production device.

4.1i Service Pack 2

Beginning with 4.1i Service Pack 2:

- If you are using ES devices, you must set the XIL_BITGEN_VIRTEX2ES environment variable. This ensures correct programming for the ES devices.

- If you are using production devices, it is not necessary to set the XIL_BITGEN_VIRTEX2ES variable in order to obtain the corrected bitstream.

- If you have previously set the variable, you must unset it.

PC Platform:


This should be done at the MS-DOS command prompt. To unset the variable via the Control Panel -> System menu tabs, remove the variable entry.

UNIX Workstation:


NOTE: Downloading an ES bitstream to a production device is safe; no damage will result, and the device will behave correctly. However, if a production device bitstream is downloaded to an ES part, the device might not behave correctly due to silicon changes between ES and production silicon. No damage will result in either situation.

4.2i Service Pack 3

The CONFIG STEPPING constraint affects the bitstream size. (Please see (Xilinx Answer 14339) for more information about the CONFIG STEPPING constraint and ways to identify devices that support different stepping values.)

If Stepping = ES or 0, BitGen will generate a bitstream of the same size as the one generated by 4.1i Service Pack 2.

If Stepping = 1, BitGen will generate a smaller bitstream size, as illustrated in the table above.

NOTE: If a "STEPPING = 1" bitstream is used on a Virtex-II device without the enhanced multiplier, DONE will go High, but FPGA logic might not function properly.

AR# 12326
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article