Re: parameter scopes for subckt instances

On Thursday 18 October 2012, Felix Salfelder wrote:
> playing with spectre netlists i came across a small issue
> about parameter scopes in subdevice instances.

I agree to make it spectre compatible.

I see a couple of issues, and solutions to them.

1.
On Thursday 18 October 2012, Felix Salfelder wrote:
> replace the call
>   subckt()->precalc_{first,last}();
> 
> with
>   assert(!_parent->subckt()->params()->_try_again);
>   _parent->subckt()->params()->_try_again =
> (scope()->params()); subckt()->precalc_{first,last}();
>   _parent->subckt()->params()->_try_again = 0;

I don't like the idea of tampering with the "_parent", then 
untampering it ..  (although I did just that in spice_wrapper, I 
couldn't figure out another way) ..

Instead, how about a second _try_again in u_parameter?  Call it 
"_try_again_2".

2.
Regarding "precalc_{first,last}" ...

_parent is not known for sure in _precalc_first.  _parent is set 
in expand, and _precalc_first is called before expand.  On the 
first pass, _parent is known to be not known.  On later passes, 
it retains a value from before.  It is best to assume that 
_parent is never known.

That is the reason for having both precalc_first and 
precalc_last.  In some cases, the behavior of expand can depend 
on parameters.  These must be evaluated in precalc_first.  In 
other cases, parameter settings can depend on what happened in 
expand.  These must be evaluated in precalc_last.  These two 
concepts are mutually exclusive, so any parameter should be 
evaluated in one or the other. In some cases, it doesn't matter.

This too suggests a second _try_again.


If there is a conflict, who wins?

parameters volts=2
subckt compon (1 2)
   V1 (1 2) vsource dc=volts
ends

subckt deeper (1 2)
   parameters volts=3
   inst1 (1 2) compon
ends

instance1 (1 2) compon
instance2 (2 3) compon volts=4
big1 (3 4) deeper
big2 (4 5) deeper volts=5