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  1. Xilinx - All Programmable
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  3. AR# 10413: 3.1i XST - Limitation of the IOB constraint with a shift register (SRL) extraction turned on.

AR# 10413

3.1i XST - Limitation of the IOB constraint with a shift register (SRL) extraction turned on.

Description


General Description:

When a shift register LUT (SRL) is inferred, the IOB=TRUE attribute does not take effect.

Solution


To use the IOB registers in this case, shift register extraction must be completely turned off. This can be done by using the attribute "shreg_extract."



For more details about the shreg_extract attribute, please see the XST User Guide at:

http://toolbox.xilinx.com/docsan/3_1i/


NOTE: This problem is fixed in the 4.1i software release.
AR# 10413
Date 07/29/2010
Status Archive
Type General Article