Too much jitter on an old HP with Athlon X2 proc

27 Feb 2018 16:14 - 27 Feb 2018 16:15 #106627 by stioc
I had an old HP desktop (DC5750 2.1GHz) lying around so I thought it'd be perfect for my LinuxCNC project (converting an RF30 to CNC) but its jitter seems to be around 94kns if I really move the windows around fast, otherwise around 55kns. It has 8G of memory, a dedicated video card (granted with only 256MB). I was a bit surprised since it seems to work/act pretty decent. I guess the question is, is the PC really unusable or can I tweak some settings (or plop in an old 60G SSD etc) that would improve the latency?

Last edit: 27 Feb 2018 16:15 by stioc.
27 Feb 2018 16:21 #106628 by Todd Zuercher
I've tried a couple of HP machines and didn't have much luck with them. The ones I tried had very limited control of bios settings, and I could not turn off power saving features to improve latency scores.
27 Feb 2018 16:44 #106630 by stioc
Thanks Todd, I'll look into the power saving features and be on the look out for another cheap desktop I can snag.
23 Mar 2018 16:23 #107754 by Hujtebesuka
see if bios let you tum off some cpu Cores and hyper-treading they improove base jittier by margin

Motherboard Bundle Intel Atom 330, 1.6 GHz, ASRock A330GC, Mini ITX
I got that one on bargin base jitter is 23000 max when i open youtube txt editors stressed it as i could comes whit parport build in if can get second hand its a good for my hobby cnc
The following user(s) said Thank You: stioc
26 Mar 2018 04:48 - 26 Mar 2018 04:49 #107890 by stioc
Thanks, the bad news is that the BIOS on these systems is lame, hardly any options to do anything. The good news however is that I fixed the latency issue and it's running great! Just cut 1/4" aluminum, a 20sec video here:

Going through dmesg stuff I realized that Debian was only seeing 4GB of memory while I recalled having 8GB as was verified by the BIOS POST. Hmm, did I download the 32bit version of linuxcnc? I opened it up and noticed that the DIMMs were mixed, 5400 and 6200. I got rid of the 5400 and also yanked the video card to go back to the onboard video (I know the opposite) but low and behold the latency dropped to 23k ns! I couldn't get it to spike beyond that. No more error messages about real time delay either. This old pc isn't ready to go to the recycle yard yet!

BTW, I noticed that even when I generated a new stepconf config based on 25k ns base jitter, in the ini file it still kept the BASE jitter to 100,000 like it was in my previous config. So I don't even know if linuxcnc really cares for anything up to 100k ns as far as its config goes.
Last edit: 26 Mar 2018 04:49 by stioc.
The following user(s) said Thank You: Hujtebesuka
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