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Xilinx Synthesis Technology User Guide

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

Log File Analysis<br />

the XC9500. In this case the HDL synthesizer will submit two new<br />

macros:<br />

• a flip-flop macro without Clock Enable signal.<br />

• a MUX macro implementing the Clock Enable function.<br />

Very small macros (2-bit adders, 4-bit Multiplexers, shifters with shift<br />

distance less than 2) are always merged with the surrounded logic,<br />

independently of the Preserve Macro or Keep Hierarchy options<br />

because the optimization process gives better results for larger<br />

components.<br />

XST messages related to CPLD synthesis are located after the<br />

following message:<br />

===================================<br />

* Low Level <strong>Synthesis</strong> *<br />

===================================<br />

The log file printed by XST contains:<br />

• Tracing of progressive unit optimizations:<br />

Optimizing unit unit_name ...<br />

• Information, warnings or fatal messages related to unit<br />

optimization:<br />

♦ When equation shaping is applied (XC9500 devices only):<br />

Collapsing ...<br />

♦ Removing equivalent flip-flops:<br />

Register equivalent to has been<br />

removed<br />

♦ <strong>User</strong> constraints fulfilled by XST:<br />

implementation constraint:<br />

constraint_name[=value]: signal_name<br />

4-4 <strong>Xilinx</strong> Development System

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