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Inherited Connections - connecting to nets

kash022

Hi All,

I have a custom design in which (due to some reason I can't remember) I have the vdd and gnd as vdd! and gnd! (please note the exclamation!) at all levels of heirarchy. Now at the top-most level, I am connecting this vdd! a net/pin called VDDpwrDDSLL and of course, I have errors.

So, to resolve this I used the netSet property. netset vdd! = VDDpwrDDSLL but nothing changes and continues to give errors. This is affecting my cdl extraction as I am getting a failed netlist.

Apart from this I tried a couple of other things like using inherited connections, but somehow it gets messy.

Any ideas on this?

Thanks,
Kashif

Parents
  • Marc Heise

    Hi Kashif,

    using the "!" on any net/pin  makes the net global and accessible through the whole hierarchy, very convenient but  also troublesome like
    you experienced since it will kind of hard-wire that connection.

    If you want to use inherited connections you need to replace all the vdd!   nets/pins  with a so called net expression. This will assign a default net and a
    handle to the net/pin.  On the level you need to make the switch you will use the "netset"  to point the handle to a new netname.

    Please check the documentation, there is a whole chapter about this.

    As workaround you could connect both nets via  0V voltage source, or use the "cds_thru" element from the "basic" library,  but this needs
    to be supported from your  flow/pdk.

    Regards,

    Marc

Reply
  • Marc Heise

    Hi Kashif,

    using the "!" on any net/pin  makes the net global and accessible through the whole hierarchy, very convenient but  also troublesome like
    you experienced since it will kind of hard-wire that connection.

    If you want to use inherited connections you need to replace all the vdd!   nets/pins  with a so called net expression. This will assign a default net and a
    handle to the net/pin.  On the level you need to make the switch you will use the "netset"  to point the handle to a new netname.

    Please check the documentation, there is a whole chapter about this.

    As workaround you could connect both nets via  0V voltage source, or use the "cds_thru" element from the "basic" library,  but this needs
    to be supported from your  flow/pdk.

    Regards,

    Marc

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