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 Constraint set up for delta and tolerance 

Last post Mon, Jan 21 2013 5:00 PM by eDaNoy. 8 replies.
Started by jemarods 17 Jan 2013 08:07 PM. Topic has 8 replies.
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  • Thu, Jan 17 2013 8:07 PM

    • jemarods
    • Not Ranked
    • Joined on Sat, Dec 1 2012
    • Baguio, Philippines
    • Posts 9
    • Points 620
    Constraint set up for delta and tolerance Reply

    Hi all,

     What is the difference of setting up a delta of 0 , tolerance of 50.... (so 0:50)

    with

    no delta, tolerance of 100...... (so :100)

    since in my case, a target appears if a delta is used.

    follow up question:, how does constraint manager identifies a target net....?

    Thanks in advance!!
    • Post Points: 20

  • Fri, Jan 18 2013 2:21 AM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,022
    • Points 17,235
    Re: Constraint set up for delta and tolerance Reply
    OK, let's say you have a 16-bit bus, a tolerance means that the length, in this case, of all 16 must be within the specified tolerance +/- 100 (:100) with no particular preference to any of the nets, called a "matched delay". As you found, a delta means that ONE of the nets is picked as a target, typically the longest unrouted but PCB Editor takes a "guess" at this and you can use right-click>Set as Target in CM if you want another target, you then get the delta and tolerance, delta could be 0, applied to the other 15 nets, with respect to the target, called a "relative delay". (See cmug.pdf, doc\cmug in the installation, page 56 for 16.6 for the description)
    • Post Points: 35

  • Fri, Jan 18 2013 3:15 AM

    • jemarods
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    • Baguio, Philippines
    • Posts 9
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    Re: Constraint set up for delta and tolerance Reply

    Thanks again sir...
    • Post Points: 5

  • Fri, Jan 18 2013 6:01 AM

    • mcatramb91
    • Top 150 Contributor
    • Joined on Thu, Jan 3 2013
    • Chelmsford, MA
    • Posts 44
    • Points 4,005
    Re: Constraint set up for delta and tolerance Reply

    I wanted to clarify a couple things:

    Setting the Delta:Tolerance field to 0.000mil:100.000mil means the longest net in the group could be 100mils longer than the target net and the shortest net in the group could be 100 mils shorter than the target.  So across all the nets you could have a variance in length as much as 200mils before seeing a DRC. (+/-100mil)

    Setting the Delta:Tolerance field to :100.000mil (blank Delta field) means that all the nets could have a variance in length as much as 100mils with no specific Target.  This is sometimes harder to match the members and could cause you to overly lengthen the nets. 

    Hope this helps,
    Mike Catrambone
    • Post Points: 20

  • Fri, Jan 18 2013 6:13 AM

    • Dennis Nagle
    • Top 200 Contributor
    • Joined on Mon, Oct 13 2008
    • Chelmsford, MA
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    Re: Constraint set up for delta and tolerance Reply

    You might want to grab a copy of the following presentation from CDNLive in 2008:

     8ICP12 : Demystifying Relative Propagation Delay Constraints

     https://www.cadence.com/cdnlive/library/documents/2008/Silicon%20Valley/8ICP12_Dennis%20Nagle.pdf

     
    • Post Points: 35

  • Fri, Jan 18 2013 2:27 PM

    • jemarods
    • Not Ranked
    • Joined on Sat, Dec 1 2012
    • Baguio, Philippines
    • Posts 9
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    Re: Constraint set up for delta and tolerance Reply

    Thanks Mike and Dennis..

     Finally figuring this out. Though sometimes I encounter this problem:

    When I set delta:tolerance, let's say, 0:50 which also means :100 (pls correct me if i'm wrong), sometimes at 0:50 setting, constraint manager reflects red colors. I think, the problem with this is the random picking of the target.

    BR

    jes
    • Post Points: 20

  • Mon, Jan 21 2013 6:42 AM

    • mcatramb91
    • Top 150 Contributor
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    • Chelmsford, MA
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    Re: Constraint set up for delta and tolerance Reply

    You are correct.  You would think that the results of using either 0:50 or :100 would be the same but the controlling factor is where the target ends up when using 0:50.  Clicking on the Length column will sort the lengths so you can see which ones are out of range of the match and where the target should be set to. Right Mouse button on the Delta:Tolerance field to set the target to works the best, that is if you don't have a target net for the group to be matched to.

    Good Luck,
    Mike Catrambone
    • Post Points: 20

  • Mon, Jan 21 2013 8:22 AM

    • jemarods
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    • Baguio, Philippines
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    Re: Constraint set up for delta and tolerance Reply

    Thanks again Mike,

     BR!
    • Post Points: 5

  • Mon, Jan 21 2013 5:00 PM

    • eDaNoy
    • Top 500 Contributor
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    • SBMA, Philippines
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    Re: Constraint set up for delta and tolerance Reply

    Good day Dennis,

     I cant access your file. I cant manage to login using my cadence account.

    Need help.

    thanks
    • Post Points: 5
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Started by jemarods at 17 Jan 2013 08:07 PM. Topic has 8 replies.