Home > Community > Forums > Logic Design > LEC - Conformal RTL to netlist mismatch

Email

* Required Fields

Recipients email * (separate multiple addresses with commas)

Your name *

Your email *

Message *

Contact Us

* Required Fields
First Name *

Last Name *

Email *

Company / Institution *

Comments: *

 LEC - Conformal RTL to netlist mismatch 

Last post Thu, Apr 3 2014 12:14 AM by Manoj Kumar S. 8 replies.
Started by hnfq 11 Jul 2012 12:21 PM. Topic has 8 replies and 4255 views
Page 1 of 1 (9 items)
Sort Posts:
  • Wed, Jul 11 2012 12:21 PM

    • hnfq
    • Not Ranked
    • Joined on Tue, Jun 14 2011
    • Posts 7
    • Points 95
    LEC - Conformal RTL to netlist mismatch Reply

    Hi, I have now seen this issue with two different designs and have not been able to figure out the root cause for this behaviour.

    I have synthesized a design using RTL Compiler and have generated both mapped and an optimized netlist.

    1. When I compare the RTL to mapped netlist (non-hierarchical comparison), I don't see any non-equivalent points.

    2. When I compare the mapped netlist to the final optimized netlist, I don't see any non-equivalent points.

    3. But when I compare RTL to final optimized netlist, I get non-equivalent points.

    Looking into this matter in detail, I noticed that these non-equivalent points start showing up as soon as I run the first incremental synthesis on the mapped netlist.

    Any ideas as to why the RTL to final netlist comparison are showing non-equivalencies?

    • Post Points: 20
  • Wed, Jul 11 2012 2:16 PM

    • bmiller
    • Top 200 Contributor
    • Joined on Tue, Oct 14 2008
    • Ottawa, Ontario
    • Posts 42
    • Points 555
    Re: LEC - Conformal RTL to netlist mismatch Reply

    I have seen this happen before too, and in my case it was caused by sequential merging in RTL-Compiler.  The two step LEC flow helps LEC resolve and verify sequential merging.  The single step verification flow can often resolve sequential merging, but sometimes it cannot.

    The two step LEC flow is the recommended way to verify RC netlists.  I suggest you continue to use the two step flow.  It is the best way to prevent false-noneqs and aborts.

     

    • Post Points: 35
  • Thu, Jul 12 2012 9:58 AM

    • hnfq
    • Not Ranked
    • Joined on Tue, Jun 14 2011
    • Posts 7
    • Points 95
    Re: LEC - Conformal RTL to netlist mismatch Reply

    Thanks for your input on the matter.

    As far as the RTL to mapped netlist comparison is concerned, should that be hierarchical or would a non-hierarchical comparison suffice?

    • Post Points: 20
  • Thu, Jul 12 2012 2:17 PM

    • bmiller
    • Top 200 Contributor
    • Joined on Tue, Oct 14 2008
    • Ottawa, Ontario
    • Posts 42
    • Points 555
    Re: LEC - Conformal RTL to netlist mismatch Reply

     Whenever RTL is the "golden" design in LEC, you should use a hierarchical compare.  This will be the most efficient, and give the best chance of a successful compare with no aborts.

     Also, this is the default when using write_do_lec.  If RTL is the golden, write_do_lec will write out a hierarchical compare script, unless you explicitly say -flat.  Similarly, if you are generating a dofile with write_do_lec and you specify a -golden netlist (such as in the intermediate-to-final comparison), write_do_lec will default to writing a flat compare script.

     Is there a reason why you would prefer a flat compare with RTL as the golden?

     

    • Post Points: 20
  • Mon, Jul 16 2012 10:16 AM

    • hnfq
    • Not Ranked
    • Joined on Tue, Jun 14 2011
    • Posts 7
    • Points 95
    Re: LEC - Conformal RTL to netlist mismatch Reply

    No, there wasn't any particular reason for running flat comparison. I just wanted to make sure that whether I run hierarchical or flat comparison I would be able to rely on the final result.

    Appreciate your input on this issue. Thanks.

    • Post Points: 20
  • Mon, Jul 16 2012 10:48 AM

    • bmiller
    • Top 200 Contributor
    • Joined on Tue, Oct 14 2008
    • Ottawa, Ontario
    • Posts 42
    • Points 555
    Re: LEC - Conformal RTL to netlist mismatch Reply

     You can certainly rely on the final result whether you run flat or hierarchical.

     If you'd like to have the option to run both ways, I suggest writing out two LEC dofiles with the write_do_lec command; one with -flat, and one without.

     But, the preferred method is to run hierarchical if RTL is golden.

    Good luck!

     

    • Post Points: 5
  • Wed, Apr 2 2014 6:07 AM

    Re: LEC - Conformal RTL to netlist mismatch Reply

     Hi bmiller,

    Can you explain what does sequential merging and sequential constanting mean?

     

    Thanks

    Manoj

    • Post Points: 20
  • Wed, Apr 2 2014 9:01 AM

    • bmiller
    • Top 200 Contributor
    • Joined on Tue, Oct 14 2008
    • Ottawa, Ontario
    • Posts 42
    • Points 555
    Re: LEC - Conformal RTL to netlist mismatch Reply

     Sure.  Sequential merging is when the synthesis tool merges two or more flops into one because they have the exact same function.  Sequential constant is when the synthesis tool optimizes away flops that are always tied to 1'b1 or 1'b0.

     

    • Post Points: 20
  • Thu, Apr 3 2014 12:14 AM

    Re: LEC - Conformal RTL to netlist mismatch Reply

     Thanks :-)

    • Post Points: 5
Page 1 of 1 (9 items)
Sort Posts:
Started by hnfq at 11 Jul 2012 12:21 PM. Topic has 8 replies.