RTAPI error and realtime delay at EMC launch

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11 years 6 months ago #57936 by Zuikkis
Huh,

I just tried with Radeon HD5450 graphics card which I borrowed from some other machine.

Now I have played youtube videos at 1080p, run some Windows crap with Wine, compiled linux kernel, etc. :)

1ms max jitter 5423ns
25us max jitter 8056ns

Woohoo! :)

So the internal graphics adapter was the real culprit, but somehow it needed the Xeon cpu before it got this bad? Or perhaps it still is somehow some BIOS setting, I did have to reset the BIOS settings when upgrading the CPU so some setting might not be as it was.. Hmmph.

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11 years 6 months ago - 11 years 6 months ago #57938 by gnagy
Yeah, I noticed major slowdown for any CPU-intensive app (ray-tracing in EQUINOX-3D) when using integrated GPUs.
The biggest downside of those GPUs is that they don't have dedicated RAM, so they use the main RAM.
What a waste to do the frame-buffer scan-out, texture access etc. at 60Hz / 1080p or whatnot on the main bus, shared with the CPU!
This can really slow down memory access for the CPU.
Different CPUs have different caches and memory access patterns, different instruction ordering and so on, so real-time apps, like stepper motor step generation can easily slow down with a faster CPU.
Superscalar / out-of order instruction execution can speed up apps overall, but instruction timing will become pretty much unpredictable. Translation: more jitter.
Some CNC machine vendors swear on staying with museum-piece in-order pentiums because of this...
Last edit: 11 years 6 months ago by gnagy.

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10 years 1 month ago - 10 years 1 month ago #79889 by Dave H
I am running an Atom D525MW MB with 4GB RAM, 60GB SSD, and onboard graphics. Max jitter base thread is always below 30000, but I still get the RTAPI unexpected error on a consistent basis with no apps running other than LinuxCNC/AXIS. Previous owner of this PC didn't have the problem, but I do not know what his settings were. Any suggestions as to what would get rid of this error?
Change base_period setting?
Get a dedicated graphics card?

Or is it a crap shoot?

Thanks,
Dave
Last edit: 10 years 1 month ago by Dave H. Reason: Left out some details

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10 years 1 month ago #79902 by tommylight
Just change the base period to something bigger and test it for a while. Raise the value gradually in increments of 10.000 till you can run the machine without getting the error.
The following user(s) said Thank You: Dave H

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