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Xilinx Synthesis Technology User Guide

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XST <strong>User</strong> <strong>Guide</strong><br />

hierarchy of your design. In addition, this constraint is<br />

propagated to the NGC file as an implementation constraint.<br />

See the “KEEP_HIERARCHY” section in the Constraints <strong>Guide</strong> for<br />

details.<br />

• Logical Shifter Extraction<br />

The Logical Shifter Extraction (SHIFT_EXTRACT) constraint<br />

enables or disables logical shifter macro inference. See the<br />

“SHIFT_EXTRACT” section in the Constraints <strong>Guide</strong> for details.<br />

• Max Fanout<br />

The Max Fanout (MAX_FANOUT) constraint limits the fanout of<br />

nets or signals. See the “MAX_FANOUT” section in the<br />

Constraints <strong>Guide</strong> for details.<br />

• Move First Stage<br />

The Move First Stage (MOVE_FIRST_STAGE) attribute controls<br />

the retiming of registers with paths coming from primary inputs.<br />

See the “MOVE_FIRST_STAGE” section in the Constraints <strong>Guide</strong><br />

for details.<br />

• Move Last Stage<br />

The Move Last Stage (MOVE_LAST_STAGE) attribute controls<br />

the retiming of registers with paths going to primary outputs. See<br />

the “MOVE_LAST_STAGE” section in the Constraints <strong>Guide</strong> for<br />

details.<br />

• Multiplier Style<br />

The Multiplier Style (MULT_STYLE) constraint controls the way<br />

the macrogenerator implements the multiplier macros. The<br />

implementation style can be manually forced to use block<br />

multiplier or LUT resources available in the Virtex-II and Virtex-<br />

II Pro devices. See the “MULT_STYLE” section in the Constraints<br />

<strong>Guide</strong> for details.<br />

• Mux Style<br />

The Mux Style (MUX_STYLE) constraint controls the way the<br />

macrogenerator implements the multiplexer macros. See the<br />

“MUX_STYLE” section in the Constraints <strong>Guide</strong> for details.<br />

5-22 <strong>Xilinx</strong> Development System

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