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Specifying Branch Topology in Allegro PCB

mvonahnen

 Is it possible to specify the topology of the routing that SPECCTRA will do in the constraint manager of Allegro?  I have seen posts about using virtual pins set up in SPECCTRA to do this, but I have not seen any examples of this being generated from contraint inputs.

 If it can be set up from Allegro, how is the branches specified so that the relative propogation delay is controlled from the branch point?  If it is not possible, is there a way of specifying this in SPECCTRA?

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  • mcatramb91

    I believe, but have not had time to verify, that if you define a Topology (ECSET) in Constraints Manager with pin to t-point Relative Prop Delay / Prop Delays that Specctra will adhere to them while Routing.  I know Cadence has gone thru many lengths to insure that the rules from Constraint Manager are passed to / aligned with Specctra so you get the rules you are looking to achieve. The other added benefit in doing it in Constraint Manager is that at least if you need to modify these critical nets in Allegro you will get DRC errors but if these rules are driven inside of a Specctra Do File you will not get any DRC errors in Allegro because the rules don't come back from Specctra.  I have many designs that use Topology driven routing with delays to t-points and I will try to make some time to do some tests then let you know how I make out.

    Hope this helps,
    Michael Catrambone
    UTStarcom, Inc.

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  • mcatramb91

    I believe, but have not had time to verify, that if you define a Topology (ECSET) in Constraints Manager with pin to t-point Relative Prop Delay / Prop Delays that Specctra will adhere to them while Routing.  I know Cadence has gone thru many lengths to insure that the rules from Constraint Manager are passed to / aligned with Specctra so you get the rules you are looking to achieve. The other added benefit in doing it in Constraint Manager is that at least if you need to modify these critical nets in Allegro you will get DRC errors but if these rules are driven inside of a Specctra Do File you will not get any DRC errors in Allegro because the rules don't come back from Specctra.  I have many designs that use Topology driven routing with delays to t-points and I will try to make some time to do some tests then let you know how I make out.

    Hope this helps,
    Michael Catrambone
    UTStarcom, Inc.

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