On Jun 11, 2007, at 10:55 PM, Jeff Trull wrote: > Hi all, > > I'm consulting for a small ASIC startup that is interested in > gEDA. They have > a handful of licenses for expensive commercial tools but were > looking for a > low-overhead way to do some semi-custom work and asked me to > investigate. I > just went through the process of figuring out how to make symbols > for the > third-party standard cell libraries they've licensed, and I thought > I'd share > my experiences since I couldn't find this described on the net > anywhere. > > Among the provided views of this library are ones for Cadence's > Composer > product. It turns out Cadence supplies a tool called "edifout", > which will > produce an EDIF (text) version of any cell view. You need to supply a > template file, which Cadence helpfully provides an example of > (tools/dfII/samples/xlUI/edifOut.il). I wrote a Perl script that > just runs > this once for every cell in the library, although some people > recommend > building a huge schematic with every cell in it, and then running > edifout > just once. With my approach you do need to generate a new template > file each > time, specifying a different cell (and you want the "symbol" view). > > Now you have EDIF for each cell's symbol view. From here I tried > to find some > kind of public-domain parser, but everything was a dead end. Then > I realized > that EDIF looked kind of like Lisp - i.e., an "s-expression". It > turns out > there's a CPAN module for parsing s-expressions called > Data::SExpression, so > I could suck in the whole file and treat it as a data structure > (lists of > lists). I did have to do a few day's worth of coding on top of > this to > generate the gschem symbols - the EDIF can be complex and the vendor > libraries are quirky. Here are a few difficulties I encountered:
I once attempted to use EDIF as an interchange format between commercial tools that supported it. It was a disaster: it would have been cheaper to chisel the design info into stone tablets and translate the result by hand. But gEDA doesn't support EDIF: why try *that* path? > ... > 3) It seems like the gnetlist backends for Spice and Verilog have > different > concepts of how ports (for example) are specified, and possibly > other things > as well. It's desirable to have a single schematic netlistable to > either > format, but I don't think that works right now. Be sure to use the spice-sdb netlister, not the old spice netlister. See http://www.brorson.com/gEDA/SPICE/t1.html. I don't know the Verilog netlister, but I think this should be a solvable problem. If I were doing Verilog, I'd want to associate ports by name (pinlabel=) rather than position (pinseq=). This seems clearer and less error prone to me. SPICE can only do this by position, so the methods would be independent. Other things might need tweaking, I don't know. But even this greying physicist whose Lisp is as rusty as the Titanic finds gnetlist back ends easy to work on. The gEDA project welcomes improvements. > > So that's what I did. I wouldn't be surprised if there are better > approaches - would anyone care to comment? Symbol creation is boring, but if you keep track of time, you'll find it's not a big part of the job. There are some tools (tragesym, djboxsym, ...) in gEDA for partially automating it. I rarely draw a symbol from scratch in gschem: I often modify an existing symbol. > I'd also be interested in hearing > from anyone else out there who's tried to apply gEDA to ASIC design. > I have, for one. See http://noqsi.com/images/ DeltaSigmaDigitization_SPIE.pdf for a description of a chip I designed with gEDA. I used OpenIP (http://research.kek.jp/people/ ikeda/openIP/) for the digital and interface blocks. Made HSPICE netlists, simulated with a spicepp-ngspice flow. The layout contractor worked from the HSPICE netlists (mine and OpenIP). The folks at Osaka also ran simulations in a commercial HSPICE (Tanner). Fab by TSMC through MOSIS. John Doty Noqsi Aerospace, Ltd. http://www.noqsi.com/ [EMAIL PROTECTED] _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
