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Unpredictable / not traceable run-time error w/ Lookahead active


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We are running a PPMAC ARM V2.3.2.5 on Phase/Servo/RTI 32/16/2 kHz, 2x3 cascaded motors (6 motors)


Running the application w/o Lookahead doesn't cause any problems.

But with Lookahead active (10ms Segmentation, 130 Segments) once in a while (every several minutes up to every several hours) run-time error occurs. Unfortunately, Coord[x].Ldata.Status always tells a 1 after such run-time error - it does not give any useful information.


What is very confusing to us is that a few milliseconds before run-time error occurs Sys.RtIntTime peaks for the duration of only 1/16 of a millisecond!!

Another characteristic is that as long Sys.RtIntTime stays below 750 us run-time error does not show up at all.

Augmenting Sys.PreCalc does not help.

Removing RtiCplc does not help neither.

At last whenever a run-time error happens it almost always shows this kind of pattern.


Today we started testings with V2.4.1.2 - results will follow.



1. Why would Sys.RtIntTime peak for less than 70us?!

2. Any suggestions which PPMAC-Variables to trace to get more useful data?


Best Regards,




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