Wednesday, October 9, 2013

orconf2013; Reports from the yearly OpenRISC conference

Dear diary,

I just got back from the yearly OpenRISC conference, orconf, which this year was situated at the university in Cambridge UK.

The conference was a great success! The flight there was not.

After forcing myself out of bed early on Saturday morning, I spent half the day in a barn on the outskirts of Göteborg, since a broken radio transmitter delayed the flight over three hours. That was enough to make me miss out the introduction talk as well as the presentations from David Greaves on a SystemC model of a multicore OpenRISC with power annotation, Stefan Wallentowitz on OpTiMSoC and Jonathan Woodruff on BERI: A Bluespec Extensible RISC Implementation. Thankfully, all talks were recorded and will be available online when they have been transcoded.

The delayed flight also made me miss the first minutes of my own presentation on ORPSoCv3, which served as an introduction to the workshop later in the afternoon. Fortunately, I had plenty of time allocated to my short introduction on the subject. The presentation was actually a bit shorter than what I had originally planned since there has been way too many other things to do lately, and I hope to have time to make a more complete introduction for next time.

After the presentations, the conference went on with a workshop based around getting OpenRISC running Linux on a DE0 nano board. Embecosm kindly provided enough hardware to let all participants team up in groups and have their own board to play with. Slightly different incarnations of this workshop has been presented by Embecosm and Julius Baxter at other events such as OSHUG, but for me it was a milestone since we decided quite recently to base the hardware workflow on ORPSoCv3, which is what I have been working on for the last few years.

It all went surprisingly well. Except for a participant who had problems with his python version, I didn't hear many complaints. Most of the credit will have to go to Julius Baxter for preparing and writing down precise instructions on how to get started, Stefan Kristiansson who prepared a precompiled OpenRISC tool chain and did a ORPSoCv3 port for de0 Nano (in 30 minutes!) and Franck Jullien who's work on OpenOCD have made debugging easier as well as providing the first ORPSoCv3 board port which was a proof that it actually worked; but it made me very happy as well, since it shows that the time I have spent on ORPSoCv3 has paid off. It's now a little easier to build and simulate an OpenRISC based SoC.

Since I don't have a DE0 nano board myself, I spent the time trying to make a port for my trusty ordb2a board based on the de0 nano port instead. It was actually my first own board port, and the process went well, but when the time came to program the board and connect to it, it turned out my development environment was not up the task, and I had to spend most of the time compiling debug software and hunting down patches. The outcome is that I now have a patch for OpenOCD to make it work properly with the ordb2a boards that I should send upstream soon.

The first day at the conference ended after the workshop, but as usual with these events, the fun doesn't stop when we leave the conference building. We all went for a fantastic dinner at St John's Chophouse where we continued to talk about everything from switching characteristics of crypto algorithms to high-level HDL languages. A few of us went on to try out some of the fine establishements in Cambridge afterwards and stopped by a pub where you could pay your drinks with bit coins. After the initial amazement of being able to pay things in real life with bit coins, this started another discussion on critical paths and process nodes for Bitcoin mining ASICs. It's funny how all conversations seem to end up in that direction.

After some well-deserved sleep, the sunday started of with Stefan Kristiansson and Julius Baxter presenting the latest improvements on mor1kx. Stefan continued the great tradition from last year of being the one who provide us with eye candy. This year he showed us Day of the Tentacle running under SCUMMVM via libSDL and glxgears running under X. These are two things that wouldn't have been possible if not for the great work on the toolchain during the last year by Sebastian Macke, Stefan Kristiansson and probably others who I probably should mention but can't remember right now. mor1kx itself has grown into a quite mature CPU now with three different pipeline implementations to cover the range from running a full-blown Linux system down to deeply embedded bare-metal applications. It has also found it's use in OpTiMSoC and will probably be the default or1k implementation in ORPSoCv3 in the near future.

Next in line was Martin Schulze who grew frustrated on the tedious work of setting up an ORPSoCv2 port for a new board and wrote a configuration system that's hooked up to Eclipse. While it might sound as conflicting with the work on ORPSoCv3, it will actually be a great combination instead, and I look forward to integrate the two efforts to make new board ports even more painless.

Last year we had a presentation where the first OpenRISC in space was unveiled, and the space theme continued in Guillaume Remberts presentation OpenRISC for space applications and EurySpace SoC. Guillaume showed clearly the advantages of using OpenRISC in an environment where failure is not an option, as it's flexible, battle proven and not tied to a single vendor.

After a well-deserved coffee break, Franck Jullien took the stage and showed the new and improved GDB. Together with his work on OpenOCD that was just accepted into upstream about a week ago, the debugging support for OpenRISC is in better shape than ever.

Last of the major presentations was Davide Rossi who talked about his group's research on extremely low power ASIC SoCs, where they had used multiple or1200 in a 28nm ASIC that will likely tape out later this year. During their work with or1200 they made several improvements to the critical path that might find it's way into the upstream or1200 repo. As there was a room full of OpenRISC experts we shared ideas on how to verify the ASIC once it was completed.

The day went on with a discussion on the feasability of an OpenRISC 1000 successor.  The idea started out a few years ago as an way to rectify some of the deficiencies of the or1k ISA, and some of the thoughts that has come up over the years are summarized on the OpenCores or2k page. The general opinion this year however was that with the current number of contributors to the OpenRISC project, it would be too much work to start a new implementation. If this was taken up as a student project or as a research project we would embrace it with open arms, so all academics reading this, please come forward.

One of the interesting things when working on a smaller architecture is that you some times realize how much the design choices of the large players are taken for granted. Sebastian Macke discovered that the way our ABI is defined differs in some regards from how ARM and Intel does things. This is usually not a problem, but combined with how some programs break the C standard for varargs in a subtle way, we have problems that only manifests itself on some architectures. Tricky! The discussion was to decide if we should change our ABI to avoid this problem, but decided against it for now to see how widespread the problem is.

Following the ABI discussion was two short lightning talks. One by Julius Baxter to show jor1k, the JavaScript OpenRISC emulator by Sebastian Macke, as it had been referred to multiple times during the conference and also to mention that most of us could be found on the #openrisc channel on The other talk was by Jeremy Bennett on the latest improvements for Verilator. Apparently verilator now supports most of the synthesizable sub set of System Verilog which is getting more and more important as the rest of the world is moving in that direction. This means that we can continue to use this fantastic tool in modern development environments, and a few high-profile projects where verilator is used was also mentioned.

To finish it all off, we had the yearly bug squashing session. Out of 71 open bugs, we were able to mark nine bugs as invalid or already fixed. Eight other bugs were repreoritized or reassigned to the right person, and I managed to fix one RTL bug in or1200 on the flight back home. In total that means we could close around 12% of our open bugs with little effort. Responding to bugs that has been reported in a timely manner is extremely important. We have previously seen potential contributors who have lost interest after seeing that their reports go unnoticed, so in addition to the yearly session, I hope that everyone goes through bugzilla from time to time to find things that can be fixed.

Flight back home was delayed once again, but we managed to catch up enough so that Ryanair could play their we're-on-time-fanfare, and once home I slept like a baby. Unfortunately, my baby didn't

In retrospect, a few interesting observations could be made from the topics of the talks. It seems that multicore OpenRISC was a large part of the presentations this year for different reasons. Stefan Wallentowitz focus was on many-core implementations, while Guillaume Rembert needed it for redundancy in fail-safe applications and Davide Rossi needed it to try out different levels of power optimizations. Hopefully, the combined work might lead things forward and having a conference like this is a great way to make people aware of each others' work. The other thing, that has also been my pet peeve and the reason for starting work on ORPSoCv3 is the need for easier system generation and interconnections.This is being addressed now, and there seem to be a lot of interest in helping out in this area.

I enjoyed the little I had time to see of Cambridge, and it's a fantastic feeling to be in the company of so many talanted persons, both from academia and industry. We were approximately twice as many as last year which also goes to show that the project has a healthy growth. This is also seen by the influx of contributors, many of who unfortunately weren't able to join us. Hopefully, we will meet next year, or at some other occasion. I hope that everyone views the recorded presentations when they become available on the conference page, as this short summary doesn't do justice to all the great talks.

Finally, special thanks should go to Julius Baxter for once again organizing the conference and making sure it's got off the ground, to the whole of Embecosm for sponsoring the event and specifically Jeremy Bennett for rounding up a few of the speakers that we otherwise would have missed out on. Also thank you to David Greaves and University of Cambridge for hosting us and taking care of thirty meek geeks during the weekend.

Hope to see you all again!