On Wednesday 05 January 2011 00:42:07 John Doty wrote:
> On Jan 4, 2011, at 5:22 PM, Matthew Wilkins wrote:
> > What are typical use cases for having multiple same-named attributes in a
> > symbol?
>
> A slotted symbol generally needs multiple slotdef attributes.
>
> A hierarchical symbol will have multiple source attributes if its
> underlying schematic has multiple pages.
>
> And nobody knows what other use cases there are, or may be in the future.
> You should make as few assumptions about how people will use attributes as
> practical.
One of the problems we have at the moment is that sometimes attributes in the
schematic override attributes in the symbol, and sometimes they don't.
Example 1. Suppose I have a "refdes=A?" attribute in a symbol. I instantiate
the symbol in a schematic, and attach a "refdes=A1" attribute to the
instantiated symbol. gnetlist (etc) will use "refdes=A1". This is overriding
behaviour.
Example 2. Suppose I have a "net=Vcc:1" attribute in a symbol. I instantiate
the symbol in a schematic, and attach a "net=Vdd:1" attribute to the
instantiated symbol. gnetlist will short Vcc to Vdd and connect pin 1 to the
shorted net. This is aggregation behaviour.
The problem with this is inconsistency. IMHO it would be better to have
overriding behaviour *only*, because in the longer term being able to reliably
override attributes would particularly be helpful in doing things like
hierarchical back-annotation and parameterised subcircuits (the latter would
be awesome for ASIC design applications, for instance). As far as I can tell,
everything that can be achieved with aggregation behaviour can be achieved
with overriding behaviour, but not the other way around.
Regards,
Peter
--
Peter Brett <peter@xxxxxxxxxxxxx>
Remote Sensing Research Group
Surrey Space Centre
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