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Nested ddt Operator

JF202408126026 1 month ago

I have a Verilog-A script that had previously been used in a competitor's tool suite without issue. In Cadence Spectre though, I have an error telling me:

Encountered nested `ddt' operator. Do not nest `ddt' operators

The offending line looks like this:

F_accel=mass*ddt(ddt(V(x)))*(V(Lin)<0.5)

I couldn't find any information in the VA standards that explains why this is a problem or what the workaround is—nothing obvious in this website either.

Any ideas?

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Kind regards,

Justin Fisher

Andrew Beckett 1 month ago

Justin,

This is covered in the Supported and Unsupported Language Elements chapter of the Cadence Verilog-A Language Reference manual (chapter 20 in SPECTRE24.1). I explain a bit about how to deal with this in community.cadence.com/.../nested-ddt-suport_ - it's all related to needing to keep track of the discipline of the intermediate result, and in our implementation you have to explicitly declare that yourself.

It's a long-standing limitation of our implementation, and happens so rarely (and is easy enough to workaround when it does happen) that fixing this has not been prioritised. By all means contact customer support (submit a support case after logging in) to request that this is fixed in Spectre.

Regards,

Andrew
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JF202408126026 1 month ago in reply to Andrew Beckett

This works!

Thanks.

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Kind regards,

Justin Fisher
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