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Inconsistent behavior of axlDBCloak?

migrg

Hi everyone,

I'm creating an array of vias using axlDBCloak. I realized that a number of my vias (seems like they are located in the same X coordinate) don't have a net associated. My code works as follows:

via_id=mrCreateViaPadstack() -> this function creates the padstack, this works fine all the time
axlDBCloak( 'mrCreateAllViasCloak(via_id))

procedure( mrCreateAllViasCloak(via_id)
...
...
axlDBCreateVia(via_id, -1497.7:10647.9, "VSS")
...

When I don't run axlDBCloak and just use the axlDBCreateVia command separately in the skill terminal everything works well. I am creating several hundreds of vias with axlDBCloak. Is there any limitation in this function? is it possible that it will 'misbehave' if it has to execute too many database accesses?

Help appreciated! Thanks!

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  • migrg

    Hi, thanks for the response. A Cadence AE helped me sort this out so I'll post here the solution in case it can help someone else eventually:

    By default, a via in an allegro database will only pick up the net of things it connects to. It doesn’t “own” a net for itself. So, if you place the via down somewhere with axlDBCreateVia and a specified net, but it cannot find a connectable object ON that net that it can hook up to, it will look for, and take on the net assignment of, anything else that it comes in contact with at that location. That could be a pin, another via, a cline, a shape, etc. In my case when the via was placed there was probably no element available there for it to connect to on that NET, but there was probably a shape on a different net, and that is what the via picked up to connect to and will change its net as a result.

    Solution to this can be to set the RETAIN_NET_ON_VIAS property on the nets in the design. This will preserve the net assigned to the via no matter what.

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  • migrg

    Hi, thanks for the response. A Cadence AE helped me sort this out so I'll post here the solution in case it can help someone else eventually:

    By default, a via in an allegro database will only pick up the net of things it connects to. It doesn’t “own” a net for itself. So, if you place the via down somewhere with axlDBCreateVia and a specified net, but it cannot find a connectable object ON that net that it can hook up to, it will look for, and take on the net assignment of, anything else that it comes in contact with at that location. That could be a pin, another via, a cline, a shape, etc. In my case when the via was placed there was probably no element available there for it to connect to on that NET, but there was probably a shape on a different net, and that is what the via picked up to connect to and will change its net as a result.

    Solution to this can be to set the RETAIN_NET_ON_VIAS property on the nets in the design. This will preserve the net assigned to the via no matter what.

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