gEDA: GenCAM

[Michael McLay <mclay-at-NOSPAMnist_dot_gov>]

The IPC Data Transfer Solutions committee has created the IPC-2500
series of standards to facilitate the manufacture and test of printed
circuit boards and printed circuit assemblies.  The first standard
that has been completed in this series is called GenCAM[1] (IPC-2511).
The IPC-2511 was developed as a replacement for Gerber photoplot
files, drill files, netlists, and assorted other formats for drawings
and data.  The GenCAM document defines a highly integrated information
model for representing PCB and PCA products.  

The GenCAM format can also represent assembly panels.  For an assembly
panel the GenCAM file will hold multiple board designs and the
placement information for the boards on the panel.  The information
model also allows for multiple builds of assemblies on a common board
to be represented in the same GenCAM file.

This standard represents several years of work by the DTS committee.
The committee included experts form OEM, equipment manufacturers, and
EMS companies.  Dozens of drafts were written and the 1.0 release came 
out in November 1998.  Work on a subsequent release started
immediately.  The 1.5 release was accepted as a new standard this
spring.  The DTS committee has agreed to not modify the information
model of the standard until after December 2001.

I wrote the conformance test software for the standard.  The
conformance test software has no copyright because it was developed at
NIST.  It is available for use and could be embedded into the gPCB or
other gEDA tools as a data reader for the GenCAM file format.  It
could also be used as the internal database for the gPCB project if
you gPCB adopted the GenCAM information model as the internal model
for the tool.

It may be useful for the gPDB package to adopt the GenCAM data model
for printed circuit design as an internal design representation
format rather than inventing a format independently.  The information
model is a consensus on the state of the art in representing PCA and
PCB designs.  GenCAM is being adopted by CAD and CAM vendors for use
in moving design data between OEM and EMS companies.  

The GenCAM file syntax currently uses a simple UTF-8 based format.
Each object instance is represented by a "keyword" statement with a
ordered set of parameter.  The DTS committee is in the process of
mapping GenCAM to XML so that the GenCAM data can easily be access by
other standards in the IPC-2500 series.  The XML mapping is a trivial
syntax change.  The conformance test software includes a demonstration
translator that converts GenCAM data to an XML file format.

The classes that implement the conformance test software were
mechanically generated from the BNF definitions defined in the
IPC-2511 specification.  The software that was used to generate the
class definitions was designed to support writing other code
generators.  We will likely use it to generate an XML Schema
definition of the information model sometime in the next couple
months.  

Further information on GenCAM is available at http://www.gencam.org/.
The IPC-2511 specification is available as a PDF file at 
http://www.gencam.org/cdrom2000/standards/ipc2511_1.5.9.pdf
There are Express-G data models of the GenCAM information model
available if you would like to see a graphical representation of the
model.  Information on the conformance test software is available at
http://www.gencam.org/cdrom2000/software/conformancetest/index.htm
It was developed on Linux and should compile out of the box.  The
binaries for Redhat are also available.  


BTW, I have been monitoring the web page for gEDA for some time and it
looked like nothing was happening.  This was especially true for gPCB.
I finally looked at the mailing list archives and found that there was
action on all fronts but the web site seems to be at the lowest
priority.  I had hoped to get gEDA involved in using the IPC standards
some time ago but up until I looked at the mailing list it didn't look
like it would be worth the effort.  It might be a good idea to at
least indicate that the web pages are not a top priority on the gEDA
home page and suggest that users search the email archives for status
information.  

-- 
Michael J. McLay
National Institute of Standards and Technology
Bld 225 Rm A57 (office), Bld 225 Rm A53 (mail)
Gaithersburg, Maryland 20899, (301)975-4099