A good Barebones PC for real time LinuxCNC

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14 Oct 2019 21:01 - 14 Oct 2019 21:20 #147887 by LuisGZ
I've been running some tests the past couple of weeks with LinuxCNC real time kernel, a Mesa 7i76e and a couple of old desktop computers just to try them out. Both of them gave me awful latency (+100k jitter), so I started testing a barebones pc (Gigabyte Brix 3150) and it was somewhat better but still bad (70k), even when I disabled most of the addon bios features.

I'm thinking on trying an Intel NUC next, but maybe you guys have some better advice?

Edit: And additional note, I'm running the Gigabyte Brix with LinuxMint due to LinuxCNC on Debian 2.9 freezing randomly in the live cd and in the actual installed system. Anyone experiencing something similar?
Last edit: 14 Oct 2019 21:20 by LuisGZ.

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14 Oct 2019 21:25 #147889 by tommylight
None of them are bad !
Since you have the Mesa card, make a simple test config with a stepgen or two and leave it on.
If Linuxcnc does not report loss of connection, you are good to go.

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14 Oct 2019 21:40 #147890 by LuisGZ
Is that so? I was under the impression a good candidate should be under 30,000 nanoseconds. Talking about my setup, I've ran long simulation paths with just 3 steppers and it never reported loss of connection, then I used an old minirouter to try a real setup and it has been working well.

I'm guess I'm being wary of the upcoming step, mounting everything on a plasma cutter and run the steppers at high velocities, I'm not sure what to expect with this setup. Should I give it a go?

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14 Oct 2019 21:49 #147891 by tommylight
Yes, yes and OH YES !
I have machines working with software stepping and base period set at 100000, happily for several years on a parallel port, they never miss a beat, ever.
This laptop i am typing on has 100 to 120K and i left it working for 5 full days with a Mesa 7i92, never fails.
Latency is very manageable even for software step generation, granted no high speeds are needed.
Mesa boards can easily do 10MHz step rates, over the network, with quite bad latency ( well under 200K tested so far ).
Stop overthinking and make the machine move, and cut parts, and enjoy.
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14 Oct 2019 22:28 #147894 by LuisGZ
That's relieving to know, thanks! Then, with your blessing, I shall kick off the project.

Just one last thing, lately I have been getting this warning when LinuxCNC starts, should I look into it?

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14 Oct 2019 22:47 #147898 by tommylight
Now that will not work ! That error can not be ignored as the latency was over 1000000 !
Did you disable everything not needed in BIOS?
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14 Oct 2019 22:51 - 14 Oct 2019 22:52 #147900 by thefabricator03
I had that error when I first started when I was trying to use a old pc with a air cpu cooler that did not have a fan attached. The computer was throttling it self down to prevent the cpu overheating giving me latency issues.

Also what is that GUI that you are using?
Last edit: 14 Oct 2019 22:52 by thefabricator03.
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15 Oct 2019 00:12 #147906 by LuisGZ
I disabled a couple of options more in the bios, and set up the fan at full speed. So far no message, I'll test it some more to make sure the warning stays off.

About the GUI, its Gmoccapy and PlasmaC with a system skin (joy blue), and some custom icons. I plan to redoing all of it, but I need to make sure the hardware works fine first :pinch:
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