Answers Database


A1.4/F1.4 MAP - 3K mapper incorrectly reports unconnected inputs to IFDs and then trims the component.


Record #4408

Product Family: Software

Product Line: FPGA Implementation

Product Part: map

Product Version: 1.4.

Problem Title:
A1.4/F1.4 MAP - 3K mapper incorrectly reports unconnected inputs to IFDs and then trims the component.



Problem Description:

This problem only occurs when you have the "Q" pin of an input
flipflop or latch directly driving the "IN" pin of an OBUFT
with *no* intervening logic. The IFD will sometimes be sucked
into the output IOB, the connection to the IPAD is lost, and
it all gets incorrectly trimmed because there is no driver.


	    IFD      OBUFT
  IPAD	    ____	    OPAD
   __	   |	|    |\      __
  |  |_____|	|____| \____|  |
  |  |	   |	|    | /    |  |
   --	   |>	|    |/|     --

	    ----     __|


Solution 1:

This issue is scheduled to be fixed in the M1.5 Performance Pack.
Meanwhile, it can be worked around by inserting a buffer between
the IFD and OBUFT. The buffer prevents the error, but is eventually
optimised away, so there is no performance loss.


	    IFD    BUFFER  OBUFT
  IPAD	    ____		 OPAD
   __	   |	|    |\     |\	    __
  |  |_____|	|____| \____| \____|  |
  |  |	   |	|    | /    | /    |  |
   --	   |>	|    |/     |/|     --

	    ----	    __|




End of Record #4408 - Last Modified: 08/05/98 16:56

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