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CTS and dontTouch Nets/instances

Rajesh Vembu

 I have a couple of questions on how CTS handles dontTouch nets/instances.

1. Assume there are pre-inserted buffers/inverters in the clock path without a FIXED attribute. However the nets belonging to them have a dontTouch attribute set.

"deleteClockTree -all"  deletes the existing buffers/inverters in the clock path if there's no FIXED attribute on them, thereby overriding the dontTouch on the nets. Is this the right behavior? 

a. Does deleteClockTree honor only the dontTouch attribute on the instance and not the nets ?

b. is there a way to instruct the deleteClockTree command to honor dontTouchNets?

2.  Will Clock Tree be synthesized if there are "DontTouch Nets" in the clock path?

If not, how to fix transition/delay violations on those nets?

 

 

Parents

  •  Kari,

    Thanks for the information. CTS does honor dontTouch nets while synthesizing the clocks.

    However, the "CASCADE" buffers seems to be inserted even on the "DontTouch" nets. Is this a bug or a feature?

    Is there a way to avoid it, other than removing the clock root from ClkGroup?

     

    Regards

    Rajesh

Reply

  •  Kari,

    Thanks for the information. CTS does honor dontTouch nets while synthesizing the clocks.

    However, the "CASCADE" buffers seems to be inserted even on the "DontTouch" nets. Is this a bug or a feature?

    Is there a way to avoid it, other than removing the clock root from ClkGroup?

     

    Regards

    Rajesh

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