2012/8/9 Peter C. Wallace <p...@mesanet.com>: > > While testing our maximum SSerial update rates, (linuxCNC 2.5.1 Ubuntu 10.4) I > noticed something somewhat interesting/disturbing about latency test on the > servo thread on my Atom 330 based motherboard (Jetway). After disabling > hyperthreading in the BIOS and adding the isolcpus=1 line to grub.cfg, the > latency test gets consistant ~6 usec max latencies. This sounds really good > but I was unable to run faster than 2 KHz servo threads without occasional > real time errors. > > To check what was going on I toggled an I/O bit at the servo thread rate and > looked at it on the oscilloscope, and the latency on the servo thread is much > worse than 6 usec, occasionally getting above 100 usec! . It gets > noticable worse when the screen is re-drawn. I do not know why the latency > test does not "see" this. > > This problem seems specific to the Atom MBs and explains why others have found > it impossible to run faster servo threads than about 1500 Hz reliably on the > Atom MBs (the newer D2500/2700/2800 may be different)
Thank You! I noticed this, when setting up my previous machine, based on Intel D525MW. I was experimenting with servo period lengths and I also was receiving realtime errors with increased servo update rate. I do not remember precise numbers, but I do know that it was between 1 and 2 kHz. I _think_ that the final value was 1,25 kHz that was working more or less stable without realtime errors. I know that I already mentioned that here on mailing list and You told me that You are running LinuxCNC with 6kHz servo rate, which confused me a lot as I was not able to get even 2 kHz. Thanks for some explanation! Fortunately I did not need increased servo update rate to improve performance, I was just experimenting. -- Viesturs If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ 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
