Cyclone III FIFO problem

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tan defaults to cutting timing between unrelated clocks.

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what do you mean with "tan defaults"?

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The dual-clock FIFO megafunction has embedded cut-path timing assignments for paths going between clock domains. The Classic Timing Analyzer (not TimeQuest in QII 7.1 SP1) uses those automatic cross-domain cuts. In the Timing Analyzer compilation report, they will be listed in the "Timing Analyzer Settings" table (example below) if they were used or in the "Ignored Timing Assignments Table" if the design didn't need them.

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+--------------------------------------------------------------------------------------------------------------------------------------+

; Timing Analyzer Settings ;

+-------------------------------------------------------+--------------------+-----------------+-------------------------+-------------+

; Option ; Setting ; From ; To ; Entity Name ;

+-------------------------------------------------------+--------------------+-----------------+-------------------------+-------------+

; Cut Timing Path ; On ; delayed_wrptr_g ; rs_dgwp|dffpipe4|dffe5a ; dcfifo_o4e1 ;

; Cut Timing Path ; On ; rdptr_g ; ws_dgrp|dffpipe7|dffe8a ; dcfifo_o4e1 ;

+-------------------------------------------------------+--------------------+-----------------+-------------------------+-------------+

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