I think we have seen issues like this (path following anomalies..) when 
there have been memory issues..

can you run some form of memcheck on it?  (for grins)

sam
On 8/5/2013 11:29 AM, Charles Steinkuehler wrote:
> How does LinuxCNC behave under heavy CPU load?
>
> I am experiencing some errors in my 3D prints that look very much like
> part of the gcode got lost or skipped over* (I'll try to post pics or a
> video).  This is happening a few times in multi-hour prints, so I
> haven't yet actually _seen_ this happen, I just see the results in the
> final print.
>
> I have not gotten any real-time errors or warnings, so I don't think
> it's anything at the HAL level or below, but on the BeagleBone, the CPU
> usage easily hits 100%, and the SD-card "hard disk" is also pretty slow
> (note that I am printing gcode files in the 2 MB to 10 MB size range,
> with lots of small line segments).
>
> Before I start seriously diving into debugging this, what is the
> expected behavior of LinuxCNC if the non-real-time task is starved for
> CPU and/or HDD bandwidth?  Is it *EVER* possible for the non-RT code to
> 'skip over' any gcode?
>
> Is it possible some delay in the non-RT code would temporarily cause a
> large following error?  That could explain what I'm seeing as well.  I
> currently have units set to mm, and the following error for each axis
> set to:
>
> FERROR =     1.0
> MIN_FERROR = 0.25
>
> Since I'm printing apx. 0.5 mm wide ribbons of plastic, if the following
> error could get big enough so the current layer doesn't stick to the
> layer below (ie: plastic squirting into free space) until the error gets
> small enough the layers overlap again.
>
> * I am printing vases, and the final print ends up with a string of
> plastic connecting two points on the perimeter of the vase, basically
> taking the "as the crow flies" direct route between two points instead
> of following the expected convex or concave curve of the vase.  The
> vases are 'organic' and curvy, so they are made up of lots of tiny line
> segments, if that matters:
>
> http://www.thingiverse.com/thing:104694
>
>
>
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