Hi, On Wed, Sep 14, 2011 at 5:38 AM, Stefan Schaal <ssch...@usc.edu> wrote: > This is a summary and conclusion of using a NI6259 with Xenomai/Analogy for > digital data I/O. First of all, many thanks to Alexis whose Analogy branch > really allowed us to succeed! We would just like share the final results of > our implementation with the hope that this might help others. > > Goals: > We needed a 19 bit parallel I/O for bi-directional communication between a > host computer and a robot controller. The 32bit DIO of the NI6259 seemed to > well suited. The communication protocol needs about 300 DIO commands per ms, > where every about 20 commands the DIO port needs to switch from write to read > and then back. > > Problems: > Initially we tried a4l_sync_dio() (synchronous communication). We measured > that one a4l_sync_dio() takes about 5us. Additionally, the switch from read > to write mode also seems to take some additional time. Thus, the > communication speed was not sufficient. > > A 2nd attempt was to use instructions and instruction lists using > a4l_snd_insnlist() and a4l_snd_insn(). We measure that this can bring down > one data acquisition to about 3.5us when all commands are queued up in an > instruction list, but due to the read/write switch we needed, we cannot use > very long instruction lists, and the read/write switch takes too long. Thus, > the communication speed did not improve a lot. > > A 3rd attempt was to use CMD structures. Following comedi examples, we create > a 200ns clock and triggered the CMD streaming with this clock. This allows > VERY fast DIO. But, again, the read/write switches that are needed frequently > made CMD structures inefficient as we could not cue up a lot of DIO commands > before the next read/write switch, and in order to do the read/write switch, > the CMD has to be aborted. We also noted that starting a CMD has some delays. > > We realized that none of these approaches was feasible. > > Solution: > We create a simple IC-based circuit that allowed to branch the read/write DIO > protocol such that we could use one DIO channel of the NI6259 for write only > (never switched to read), and the 2nd DIO channel on the NI6259 for read only > (no switching). By avoiding the read/write switching, all three ideas from > above are possible and run fast enough (after some optimization of our > communication protocol). We ended up using a4l_sync_dio() as it is the > easiest to use, and yielded sufficient speed. With the CMD approach, we would > be able to go a factor 5-10 faster even. > > For you info, our interface C-code is attached. This is not general purpose > software, but should allow other to get the idea of what we do.
Many thanks for this feedback! > > Best wishes, and thanks again to Alexis! > > -Stefan > > Alexis. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
