A quick question, youre running preempt-rt on a raspberry pi, I might be wrong on this, but I think there is a patch for the linux kernel lowering the latency for context switching by running in a single virtual adress space .... ( ie. the arm doesn't have to copy the caches when it context switches ). If the patch is appliable to your cpu it would lower latency MUCH.
If not I am barking up a tree ...... :-D .... I don't remember much but it was similar to this, worth checking out .... http://www.denx.de/en/pub/News/Xum2009AbstractsAndPresentations/The_ARM_Fast_Context_Switch_Extension_for_Linux.pdf Were talking ARM 5 here .... / regards, Lars Segerlund. 2012/9/8 Michael Haberler <mai...@mah.priv.at>: > I've done some bit-bang timing measurements for the Raspberry GPIO pins > > see > http://linuxcnc.org/index.php/english/component/kunena/?func=view&catid=18&id=20514&limit=6&start=48#24062 > > I'm not saying the Pi has many cycles left at 220nS transition spacing, but > the 'slow ARM IO myth' seems to be just that, memory mapped IO is roughly an > order of magnitude faster than I ever got with a PC parport driven from a > user process; interrupt latency is another issue but GPIO in this style > doesnt use it > > - Michael > > > Am 20.07.2012 um 16:30 schrieb Charles Steinkuehler: > >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> On 7/20/2012 9:11 AM, Kent A. Reed wrote: >>> On a more serious note, as has been discussed on the two emc mail >>> lists, the road to ARM is littered with ideas but so far we have >>> little result. >>> >>> The nicely done miniEMC2 project by Sergey Kaydalov is the most >>> complete effort I know of. It employed the higher-latency Xenomi >>> code rather than RTAI. Inquiring minds want to know more about the >>> possibility of porting this code or something like it to boards >>> like the RPi or BB and about the resulting performance attainable. >>> I wish I could have tackled this already but I've got too many >>> family issues at the moment. >> >> I'm planning on trying to use the PREEMPT_RT version of LinuxCNC with >> my Pi when it comes in, but I'm not sure what sort of latencies to expect. >> >> On conventional PC hardware, I've gotten decent latency jitter with >> modern systems, but not yet down to the RTAI levels. On older >> hardware latency with PREEMPT_RT is much worse, particularly on >> single-core systems (although I don't yet know if this is due to not >> having two cores to schedule between or because all my single-core >> systems are pretty ancient). >> >> I'm also hoping on the Arm it might be possible to use the fast IRQ >> and read/write the I/O pins in an ISR which may allow the servo thread >> to run with much higher jitter. >> >>> Then there's the problem of gluing these boards to our CNC hardware >>> about which I yield to Jon. >> >> My current plan is to bit-bang GPIO pins based on code from the >> parallel port driver, but adding a bit of electronics would probably >> make things much easier. I'll evaluate that option once I see where I >> get with software stepgen. >> >> - -- >> Charles Steinkuehler >> char...@steinkuehler.net >> -----BEGIN PGP SIGNATURE----- >> Version: GnuPG v1.4.11 (MingW32) >> Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ >> >> iEYEARECAAYFAlAJa6IACgkQLywbqEHdNFyNjwCfTVchMrwrcmA2RZ78hoYM0OEa >> zn0AoOyTZa74B1MnFaDOL2HqUxG5LwOH >> =Dmby >> -----END PGP SIGNATURE----- >> >> ------------------------------------------------------------------------------ >> Live Security Virtual Conference >> Exclusive live event will cover all the ways today's security and >> threat landscape has changed and how IT managers can respond. Discussions >> will include endpoint security, mobile security and the latest in malware >> threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ >> _______________________________________________ >> Emc-developers mailing list >> Emc-developers@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-developers > > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
