Dynomotion Forum

Getting lots of "Unexpected Coordinated Motion Buffer Underflow!" modal dialog boxes, with the associated interruption of G Code execution. Pressing OK never restarts motion.
Is there a way to automatically launch both KMotionCNC.exe and KMotionServer.exe with Above normal Base priority?

I've looked at;
https://answers.microsoft.com/en-us/win ... b2611926ad
https://arstechnica.com/civis/viewtopic.php?t=328353
https://www.sevenforums.com/tutorials/8 ... -menu.html

Running KMotionCNC version 435d on an older PC;
Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz 3.19 GHz
8.00 GB (7.68 GB usable)
SSD 256GB
64-bit operating system, x64-based processor
Windows 10 Pro, version 21H2

I think the Tool Setup | Trajectory Planner | Trajectory Planner settings are optimized;
Break Angle 179
Look ahead 8
Collinear Tolerance 0.001
Arcs to Segments checked
Corner Tolerance 0.005
Facet Angle 1.2

Tool Setup | Trajectory Planner;
Arc beg/end radius Tol 0.008
Arc radius small Tol 1e-12

Hi

Sorry to hear you are having problems.

That actually seems to be a very capable PC.

The parameters all seem very normal and conservative. Except the Arc beg/end radius Tol 0.008 seems large.

Anything special about your GCode? Is the problem reproducible?

You might try V4.35f (although I don't recall any related issues)

Thank you for such quick reply!

The PC is 12 years old (Lenovo M90P 5536A1U ThinkCentre). It doesn't score very high;
https://www.userbenchmark.com/UserRun/51343260
More stats;
Intel Core i5 650 @ 3.20GHz, Clarkdale 32nm Technology
8.00GB Dual-Channel DDR3 @ 665MHz

I write GCode by hand (mostly 2.5D, so loops, variables, and subroutines are very useful). I recall increasing the "Arc beg/end radius Tol" because I was getting compile failures during KMotionCNC simulations (I use offset lines in the CAD model to find tool positions between lines of GCode, and I presumed these errors were due to rounding errors). I'll decrease it to 0.001" (from 0.008) and see what happens.

No pattern to the "Unexpected Coordinated Motion Buffer Underflow!" modal dialog boxes. I've run a simple program (a figure 8 - two circles - in the XY plane, with a Z move out of plane at each extreme; a figure 8 tilted 45 degrees) for hours trying to reproduce the error. Sometimes it happens often, sometimes not at all, hence my suspicion that it has to do with background activities in Windows (which running both of your EXEs at a higher priority might fix, or at least reduce the frequency of, but I haven't run the tilted 8 at higher priority - I'll report back).

I doubt if it is a processor or priority issue.

Possibly a Windows Driver issue where it locks up the PC for 8 seconds? 1 second lookahead is normally sufficient. You might try changing that to 1 seconds to see if it is better or worse.

You might verify if it is really a buffering issue or whether KFLOP is being reset. KMotionCNC might be misinterpreting a reset as a buffer problem. Have your initialization program turn off one of the LEDs (Bit46) and after an error if the LED comes back on you will know that KFLOP was reset.