Re: [IBIS] Port type with [External Circuit]

Arpad:

A clarifcation per suggestion 1. is reasonable.

You can make proposals regarding declaring the port type
for user-defined ports.  I think this will take some work
and require revisiting a lot of old issues since a method
already exists for converting ports using D_to_A and A_to_D.
So, some implicit declaration method is already available.

Bob


Muranyi, Arpad wrote:
> Hello IBIS fans,
> 
> We discovered a potential problem with the port types when using
> [External Circuit]s.
> 
> The "Ports under [Model]s" section of the spec discusses the naming
> convention of the reserved port names used with [External Model].
> 
> | The first letter of the port name designates it as either digital ("D") or
> | analog ("A").  Reserved ports 1 through 13 listed above are assumed or 
> | implied under the native IBIS [Model] keyword.
> 
> Later, the "Ports under [External Model]s" section describes the port name
> rules for [External Circuit]s:
> 
> | The [External Circuit] keyword allows the user to define any number of ports
> | and port functions on a circuit.  The [Circuit Call] keyword instantiates
> | [External Circuit]s and connects their ports to specific die nodes (this can
> | include pads).  In this way, the ports of an [External Circuit] declaration
> | become specific component die nodes.  Note that, if reserved digital port
> | names are used with an [External Circuit], those ports will be connected
> | automatically as defined in the port list above (under [External Circuit],
> | reserved analog port names do not retain particular meanings).
> 
>>From these sections of the spec we know how to deal with the ports of
> [External Model]s, i.e. it is known what their type is, but there is a
> problem with [External Circuit]s.
> 
> Other than the usage of the reserved digital port names, there is no way
> of knowing what the port type is for a user defined port name, because we
> do not have a mechanism to declare port types in IBIS.  Unfortunately the
> [Node Declaration] keyword doesn't do more than list the die nodes and/or
> pads, so this keyword would not be useful to find out what the type of a
> port may be that is connected to it.
> 
> This is a problem, because some tools need to know the type of a port in
> order to know how to connect things.  Looking into the [External Circuit]
> to find out the port type may not be as easy as it sounds either if only
> compiled (or encrypted) models are available.
> 
> I would like to make two suggestions:
> 
> 1)  If the "first letter rule" was only intended to apply to the reserved
> port names (to be honest, this is not 100 % clear to me from reading the
> spec.) we need to write a clarification BIRD to clear this up.
> 
> 2)  If the "first letter rule" doesn't apply to user defined port names,
> I would propose that we invent a port type declaration mechanism to declare
> the user defined port types.
> 
> Any comments or questions are appreciated.
> 
> Thanks,
> 
> Arpad



-- 
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
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bob@teraspeed.com

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