Successfully configured with stepconf: but +Y-axis "stutters" running G-code

Shortest: Why is my machine "stuttering" in the +Y direction when running G-code, but not when jogging?

I've had to replace one old HP pc with an old Dell pc when the former's motherboard failed.

So far I've managed to install a RT-PREEMPT version of Ubuntu/Linux Mint 20.4 and have compiled LinuxCNC pre2.9 for that, and it runs, in the sense that LinuxCNC can jog my gantry router around in all 3 axes.

I decided to run the LinuxCNC-logo demo/splash demo program, after making some safety edits, like settting feed limits, and an odd noise during the run was traced to executions of Y-axis moves in the positive direction.

The machine sounds like it's "stuttering", and in fact is visually "backing up" after every move of about 1/4".

I should say that:
* the old machine was running lxcnc 2.8, the config files of which have been copied over
* had two parallel-port PCI cards, which have been moved over
* the machine jogs perfectly happily in all six directions
* latency seems acceptable, and tests of all 3 axes showed no surprising behavior in stepconf
* commanded MDI/F5 moves of e.g., G90 G55 G1 F50 +Y2 execute normally without the noisy behavior
* a copy/paste of a susceptible line in the G-code to the command line also runs without the behavior
* the LinuxCNC logo demo G-code was run in G21/mm mode because I had not noticed it to change it

Is this type of "stuttering" a known symptom of something?

Thank you.

There are striped lines on the base period side, this will show the value.

tommylight wrote:

Code:

latency-histogram --show There are striped lines on the base period side, this will show the value.

Firstly
 

Firstly, I apologize for disappearing for several days.  I thought I noticed something that let me proceed to try vainly to meet a deadline yesterday.  I had partial success, but ultimately called it quits late last night.

Secondly, thank you for your help.

I've attached the latest latency-histogram with an even heavier torture test going on.

I see three ways forward for meJ: 1. continue on the path of trying to find and fix the sources of latency, 2. dial back performance settings to avoid being hit by latency problems, or 3. start over.  Of course, I'm partial to #1 because it would be better to have a better understanding of my setup.

I can add now that the original problem I mentioned did not recur, after simply editing the LinuxCNC logo G-code program to change G21 to G20 (and adjusting the scale accordingly), mm to inch mode.  It ran without incident in inch. 

What caused me to throw in the towel last night was this: after experiencing a Z/joint-2 following error when jogging (at under 200 IPM) and losing position information and having to restart LinuxCNC, I had actually been able to face the workpiece (w/a program of simple back-and-forth passes).  However, as I was jogging to set the zeroes for the first roughing pass of a model, it lost position again, this time in the Y-axis.  While I suspect the rough pass might have run successfully, I couldn't be sure and I still have the more complicated finish pass to run (which actually might run fine owing to the much fewer and shorter rapids).

To recap:
1. I have copied the config/ directory from the old machine to the new, and have edited only the parport/io addresses,
2. move the PCI (not PCIe) parallel-port cards from the old machine to the new.
3. run stepconf and tested all 3 axes in the back-and-forth mode, confirming I thought the acceleration entries were acceptable.
4. the machine stops abruptly, but not predictably, when jogging (at least in Y and Z so far) with a "joint-following error."

 

Oh, I see, finally, the striped lines you mentioned (attached).

(I then did a websearch for +linuxcnc +histogram +"striped lines" and... found only this post. :^\ )
 

Yeah that is bad, see the red numbers in the histogram, those are huge latency excursions so it will be useless for anything except testing.
That will cause random stalls, wrong dimensions, low motor torque...
If you can:
-remove all memory sticks and test them one by one
-change the power supply
-check the processor for heat or failed fan, repasting it might help a lot
-test the latency from a live USB session
Also remove cpu isolation, some insist it works, for me it never made any reasonable difference with RT kernel, it does work with RTAI.... Thinking of it there is a RTAI kernel that works with the official ISO, so try that, chances are it will work.
linuxcnc.org/docs/2.8/html/getting-start...#cha:Installing-RTAI

Oh, yes! I was staring at the figure for clues, but agree, even if I missed the significance of "all-red" numbers, four "off-charts" ought to have made an impression on me.

I'll try, in this order:
* resetting isocpus (to elimate the other one, and then neither)
* test the memory sticks
* CPU processor heat
* latency from a LiveDVD session (it's what I have)
I know I won't change the power supply. I'll get another box from the friend.
The same goes for an RTAI kernel. I'll first try to replicate what I've got on the other box which should tell me if it's the hardware that's responsible.

Thank you for a Way Forward.

BTW, I also found Rod's post regarding "Latency" . In my opinion, it is definitive and ought to be a Sticky.