On Saturday 12 June 2010, Slavko Kocjancic wrote:
>Hello...
>
>Just one question.
>What even't triger RTAI error message Unexpected latency error message
>(showed only once)
>I know that is report of lattency problem but when is trigered?
>I have base thread on 25uS so is this triggered when jitter is more than
>25uS or what?
>
>I have laptop for running EMC. If I startup computer and immediatly
>start EMC I got that error and if I start lattency test right on startup
>then I got lattency in range of miliseconds. But after few minutes they
>dissapear and then latency stay in 15uS range (glxgear running over the
>30hour test) I suspect that this is caused as the laptop has no battery
>(was death) and when charger abort charge the latency problem is solved.
>
>Just now I had problem (once) that Z axis was'nt goes up and I broke
>drill bit. So I don't know what cause that. I suspect if that is jitter
>problem (over 25uS) i should got message about that but here are no
>message. I know I have underpowered Z stepper but also have slow
>acceleration and speed. I't never bind till now.
>I use phase drive so step/dir timing's isn't cause.
>
>Slavko.
The latency error is only reported once, the first time it happens, mainly
because the output process to tell you adds to the problem. So it is
occurring later even if not reported.
Set your BASE_PERIOD for say 50us, and the servo loop time for at least 10x
that. Try this, and reduce the BASE_PERIOD 5u-secs at a time until you can
just barely note that the machine feels busy and keyboard response loses its
instant feel. Add the last 5u-secs back and leave it there. This has
worked well for me, on an old Athlon running at 1.6Ghz.
Longer BASE_PERIODs will have a noticeable effect on how the motors sound at
higher speeds because it limits the size of the speed step available and you
hear the motors stepping up and down like 2 or 3 key gaps on the piano
keyboard. The shorter BASE_PERIODs will make this smoother, and because the
motors can follow these smaller steps easier, you can get higher speeds. I
have also, at least on my little machine, found that setting the
accelerations to smaller values so you hear the motors winding up and
unwinding, also helps to achieve the higher speeds. This, like everything
else has trade offs because the smaller motions never get to a very high
speed.
Your broken bit because Z didn't retract was probably caused by the
combination of a too high acceleration setting, combined with MAX_VEL also
being too high, and when one of those latencies hit, the motor went out of
sync & stopped, and the next pulses after the latency hit were too fast for
the motor of follow from a dead stop.
So the first thing is to find out where the latency is. Personally, the
least interfering video driver (which causes 75% of these problems, and poor
APIC hardware is often found) turned out to be the vesa driver. The nvidia
driver was by far the worst, the nv driver was better, and the vesa driver
was hand downs the best. YMMV of course. I haven't ever had an ATI card in
that machine, just a series of nvidia cards, which have a limited lifetime,
those with fans only last as long at the $0.65 fan they use on them.
APIC related problems are best treated with a different motherboard.
Somewhere in all the above rambling might be something helpful. I hope so
at any rate.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
I'm going to live forever, or die trying!
-- Spider Robinson
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