Pc Requirements

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Latency-Test

By preforming a latency stress test we are able to check if the desired PC hardware is capable to have a good performance when running LinuxCNC. This test returns the maximum deviation time

Latency-test gets the time and subtracts from it the previous time the same thread started. It determines the maximum deviation (both larger and smaller) of this difference compared to the selected period, compares the absolute values of the two deviations, and reports the larger absolute value as the max jitter. [1]

So, what do the results mean? If your "Max Jitter" number is less than about 15-20 microseconds (15000-20000 nanoseconds), the computer should give very nice results with software stepping. If the Max Jitter is more like 30-50 microseconds, you can still get good results, but your maximum step rate might be a little disappointing, especially if you use microstepping or have very fine pitch leadscrews. If the numbers are 100 uS or more (100,000 nanoseconds), then the PC is not a good candidate for software stepping. Numbers over 1 millisecond (1,000,000 nanoseconds) mean the PC is not a good candidate for LinuxCNC, regardless of whether you use software stepping or not. [2]

In our case, we will use Mesa boards, so the control signals will be not software, but hardware generated, so the values of latency are less (but still) important.


PC specifications

Pcspecs.png


Boot usb live pen

After a creation of the usb live pen, insert the pen in the PC usb plug.

Penusb.jpeg

Now press the PC power button and enter in the motherboard boot menu, typically pressing F8, F11 or F12

Bootmanager.jpg


Boot options

In this fist aproach to determine the latency values, LinuxCNC will run on live version instead of a permanent install.

Bootoptions.jpg

Latency results

Now is time to run the latency test. During the test is important to stress the PC to the maximum. We are looking to the worst case scenario (higher values of latency).

Runlatency.png

We open several youtube videos and copy large files at the same time during this test. And we got the following values:

Latencyresults.png

The max jitter value is less than 15000ns, so we are ok with this machine to run LinuxCNC.