Re: Verilog-AMS Committee Meeting Minutes - Dec 22 2006

Dave Miller wrote:

> edaorg@v-ms.com wrote:
>
>> Boris Troyanovsky wrote:
>>
>>> If concurrent multiple analog blocks are incorporated into the 
>>> standard,
>>> then I think it should be possible to formally prohibit constructs that
>>> result in indeterminate switch branch values. The standard currently 
>>> says
>>> (5.3.1.3):
>>>
>>> "It is illegal to contribute to an external switch branch from 
>>> within an
>>> analog block."
>>>
>>> [ Presumably, this means to contribute via a hierarchical out-of-module
>>> reference. ]
>>>   
>>
>> IMO the statement in 5.3.13 is fairly meaningless: there is no way 
>> from within a module that you can tell that a branch you are 
>> connecting to is a switch branch in some other module (doesn't matter 
>> if it's OOMR or not). So if it is illegal it's going to be a 
>> elaboration/runtime error, but personally I see no reason for it to 
>> be illegal. I'd vote for striking the sentence.
>
>
> Well I'm not too sure on that, I think that is very implementation 
> specific. 

It's only implementation specific if the implementation can't do switch 
branches, but I'd assume most can since switch branches are allowed. The 
only bad case for switch branches (causing a elaboration/runtime error) 
is if you have multiple different potentials applied to the same branch, 
but for the case which is ok (you have multiple potential contributions 
of the same value)  it's the same as having one, i.e. the simulator 
never has to deal with solving more than one switch contribution on a 
branch .

> I can certainly tell if a hierarchical contribution to a branch turns 
> it into a switch branch.

I think you may have the wrong definition of "switch branch", it's not a 
switch branch unless the contribution from an analog block can actually 
switch between potential and flow. It's problematic for the simulator 
because it may have to restructure the matrix used to solve the circuit 
when the branch usage changes.

> I would certainly prefer to keep a restriction in place that prevents 
> users contributing hierarchically to switch branches. It seems to me 
> that it would be more likely something they would do accidentally, so 
> would probably like to be warned about it.
>
> Dave

I have no problem with issuing warnings.

Kev.