Mail Archives: geda-user/2016/01/02/13:53:44
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On Jan 2, 2016, at 11:16 AM, John Griessen <john AT ecosensory DOT com> wrote:
> On 01/02/2016 11:55 AM, DJ Delorie wrote:
>>> I agree, refdes is good choice.
>> Note that giving refdes this special meaning, means that gate =
swapping
>> (or sharing, across heirarchy instances) between packages is no =
longer
>> an option. Is that a reasonable compromise?
>=20
> I had never thought of hierarchic board schematic or layout this way =
before just now.
One example is a recent project where I had a subcircuit that needed =
three sections of a quad NAND, U6. The next level up used two instances =
of the subcircuit, X1 and X2, and it also happened to need two NAND =
gates. So, I set refdes=3DX1/U6 and refdes=3DX2/U6 in the higher level, =
and it all worked. But that=92s a special trick, not generally =
applicable in all cases.
>=20
>=20
> I suppose it might have value, but I mostly thought of hierarchy in =
packages on boards
> as a way to quickly design, no more.
In ASIC design, the hierarchy corresponds to cells in the layout. But =
there, you don=92t have slots. Perhaps the most annoying common case for =
me in PC board design is when I have a lot of channels and each one =
needs three sections of a quad. In PC board design, you=92d really like =
to be able to choose the convenience of a common cell layout or the =
economy of sharing packages between instances.
> There is a negative in many instances where you
> would do multiple channels -- anything analog. spaghetti of utilizing =
nearby groups for
> tighter layout and autorouting could easily give simulation changes =
and crosstalk changes that are unwanted.
>=20
> Would you have the group top level definition be an attribute also? =
It could be good in a sea of
> dual and quad gates that are digital switch glue next to some analog. =
In such a case you would want to separate
> analog and digital into two modules that are always adjacent, and only =
allow the swapping in the digital parts.
>=20
John Doty Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com
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