[Magic-dev] scmos-tm.tech drc question

[R. Timothy Edwards]

Dear Bertrand,

> Looking into the scmos-tm.tech file I came across the following 
> observation:
> 
> The layer "pad" is defined on the metal2 plane. It is not defined as a 
> contact.
> However, on line 3000 of the scmos-tm.tech :
> 
>     spacing 
> pdc/m1,ndc/m1,psc/m1,nsc/m1,hpdc/m1,hndc/m1,hpsc/m1,hnsc/m1,pc/m1,ec/m1,capc/m1,clc/m1,emc/m1,pbc/m1,nbdc/m1,m1,m2c/m1,gc,pad/m1 
> pdc/m1,ndc/m1,psc/m1,nsc/m1,hpdc/m1,hndc/m1,hpsc/m1,hnsc/m1,pc/m1,ec/m1,capc/m1,clc/m1,emc/m1,pbc/m1,nbdc/m1,m1,m2c/m1,gc,pad/m1 
> 2 touching_ok "First-level metal spacing must be at least 2 (MOSIS rule 
> #7.2)"
> 
> there are statements referring to pad/m1.
> 
> However I have checked that pad spacing to metal1 violations are not 
> reported.
> Is this the intended behavior ? If so, should magic report a problem 
> during reading the technology file ?

If the pad is really defined on metal2, then "pad/m1" can only be an
empty set.  However, other places in the techfile (such as, most
importantly, the operations in "cifoutput") define "pad" to cover
metal1, m2c, metal2, m3c, and metal3 (a standard full stackup for
processes that don't have many metal layers and/or thick top metal).
I'm really not sure why "pad" is not defined as a contact between
metal1, metal2, and metal3.  In the source (magic distribution,
file scmos/scmos.tech.in), the last line of the "contacts" section
is
		pad	metal1 metal2 metal3

and has been commented out.  I am wondering when this was commented
out.  Most of the pad rules (cifoutput, drc, extract) only make sense
if "pad" is defined as a contact this way.  I checked that the comment
exists in distributions as far back as version 7.1.5.

If you add the line above (or uncomment it from the source and re-install)
then everything seems to work okay.

Can anybody confirm if the "pad" line is in the techfile "connect"
section prior to version 7.1.5?  It appears to predate my implementation
of stacked contacts, although that doesn't guarantee that it wasn't
something I did once for a test and forgot to put back the way it was.

						---Tim

+--------------------------------+-------------------------------------+
| Dr. R. Timothy Edwards (Tim)   | email: tim at opencircuitdesign.com    |
| Open Circuit Design, Inc.	 | web:   http://opencircuitdesign.com |
| 22815 Timber Creek Lane        | phone: (301) 528-9364               |
| Clarksburg, MD 20871-4001      | cell:  (240) 401-0616               |
+--------------------------------+-------------------------------------+