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Stack via on spare gates' pins

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Hi layout-ers!

Need your advise on implementing an requirement for spare gate.

I need to put some spare gates in the design; I can do this, and place it well.

However, there is a requirement that the pins of the spare gates (input and output) should have a stacked via on top of its an all the way to the top metal. This is to increase the chance of changing less metal layers when eco is using the spare gates.

So, I need to

1. Do not place the spare gate under power stripes (if not the stacked via will short to the power (input pins are connected to tie-high/tie-low)
2. find a way to add the stacked via on the pins (and even better the gloabl router is able to optimise the routing for congestion with the existance of these stacked via)

One easier way is to create standard cell with those pins; but unfortantely  the standard cell library I am using does not have these features, and I do not wish to create new cells with the stacked pins...

Anyone done this before and know the correct way to do this in SOC? Thanks.

Regards,
Eng Han


Originally posted in cdnusers.org by EngHan
Parents

  • Hi Mohan,

    Thanks for the tip. But I think you miss my point.

    The main concern is how to add stack via on top of the pins of the spare gate (and not placing the spare gate).

    I believe that SOC does not have direct command to add stack via on the pins. I can write some code to do this, but I wish to know how other people do this (I have learnt this requirement several years ago, but I personally is doing this the first time) before I spend time in the coding.

    However, I understand that with this requirement, there are added restriction to the placement flow. Firstly, I think the option "setPrerouteAsObs" is too restrictive as it also prevent non-spare-gate to be keep out of power stripes, result is huge loss in untilizaiton. Secondly, the stack via can only be added after placement (infact after cts, and possibility just before detailed route), the global router don't see this and cannot optimise the congestion with these stack via. I hope there is some smarter way to implement the flow.


    Regards,
    Eng Han


    Originally posted in cdnusers.org by EngHan
Reply

  • Hi Mohan,

    Thanks for the tip. But I think you miss my point.

    The main concern is how to add stack via on top of the pins of the spare gate (and not placing the spare gate).

    I believe that SOC does not have direct command to add stack via on the pins. I can write some code to do this, but I wish to know how other people do this (I have learnt this requirement several years ago, but I personally is doing this the first time) before I spend time in the coding.

    However, I understand that with this requirement, there are added restriction to the placement flow. Firstly, I think the option "setPrerouteAsObs" is too restrictive as it also prevent non-spare-gate to be keep out of power stripes, result is huge loss in untilizaiton. Secondly, the stack via can only be added after placement (infact after cts, and possibility just before detailed route), the global router don't see this and cannot optimise the congestion with these stack via. I hope there is some smarter way to implement the flow.


    Regards,
    Eng Han


    Originally posted in cdnusers.org by EngHan
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