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 Two warnings(external_delay and CSA rejected) 

Last post Thu, May 9 2013 6:04 AM by grasshopper. 1 replies.
Started by 20050710212 08 May 2013 05:47 AM. Topic has 1 replies and 613 views
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  • Wed, May 8 2013 5:47 AM

    Two warnings(external_delay and CSA rejected) Reply

    There are two kind of warnings always happened during synthesis. I checked them in the user manual but I do not know how to solve them. 

    1. The following primary outputs have no clocked external delays.  As a result the timing paths leading to the ports have no timing constraints derived from clock aveforms. The'external_delay' command is used to create new external delays.
    /designs/FIFO/ports_out/dataout[0]
    /designs/FIFO/ports_out/dataout[10]
    /designs/FIFO/ports_out/dataout[11]......


    2.There is 1 CSA group in module 'FIFO_csa_cluster_33'... Rejected. Somtimes it is accepted. sometimes it is rejectd.                          What is CSA group?

    Could you please give me some advieces to fix these problems?

    Thank you very much.

    • Post Points: 20
  • Thu, May 9 2013 6:04 AM

    • grasshopper
    • Top 25 Contributor
    • Joined on Fri, Jul 18 2008
    • Chelmsford, MA
    • Posts 242
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    Re: Two warnings(external_delay and CSA rejected) Reply

     Hi 20050710212,

     (1) As the message specifies, the outputs have not clock reference hence no way to time paths ending at those outputs. You need to ask a set_output_delay statement in your SDC with a clock reference if you expect those paths to be timed

    (2) Carry Save Adder. Do a google search on it and you will get plenty of detailed information on adder architecture. Acceptance/Rejection depends on a variety of things, mainly your design constraints

    hope this helps,

    gh-

    • Post Points: 5
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Started by 20050710212 at 08 May 2013 05:47 AM. Topic has 1 replies.