Help determining latency and EMC timing parameters....

[margni74]

I'm trying to determine the latency numbers for my machine.. I ran 'latency-test' with an older Althon XP 1.350Ghz w/256MB Mem....and got the following from the window that popped up:

Maximum Jitter
Servo Thread: 48686
Base Thread: 61464

Max Interval
Servo: 1045191
Base: 85769

How do I apply these numbers to the StepTimingCalculator spreadsheet:
From the G320 specs:

Step Pulse Frequency 0 to 250 kHz
Step Pulse “0” Time 0.5 Microseconds Min.
Step Pulse “1” Time 3.5 Microseconds Min.

I can then fill in Required Step Length and Required Step Space... not sure what to put for 'Required Direction Setup', 'Required Direction Hold'. I guess 'Worst Case Latency' is derived from the output of 'latency-test'???

[margni74]

anyone??

[chester88]

Have you read this?
http://wiki.linuxcnc.org/cgi-bin/emc...StepGeneration
Worst case Latency comes from the latency test.
'Required Direction Setup', and 'Required Direction Hold' are special setting for drives that need extra time to for those comands.

[Big John T]

Interesting that the G320 manual does not mention the direction setup and hold times. You might do a search in the Gecko forum to see what you find or ask directly in the Gecko forum. When you find out I'll update the wiki site step direction page:

http://wiki.linuxcnc.org/cgi-bin/emc...r_Drive_Timing

It is much less painful to get a step direction config going if you just use the Stepconf Wizard do generate your config files. Then you can add to or modify the custom files as needed.

Take a look at this short getting started guide.

http://www.linuxcnc.org/docs/EMC2_Getting_Started.pdf

A SWAG on your direction setup 1000us and 20000us for direction hold.

John

[margni74]

Originally Posted by chester88 Have you read this? http://wiki.linuxcnc.org/cgi-bin/emc...StepGeneration Worst case Latency comes from the latency test. 'Required Direction Setup', and 'Required Direction Hold' are special setting for drives that need extra time to for those comands.

Thanks for the info... btw, it looks like 'latency-test' doesn't actually spit out the worst case latency #'s... It appears that you have to actually run :
sudo mkdir /dev/rtf; sudo mknod /dev/rtf/3 c 150 3;
sudo mknod /dev/rtf3 c 150 3;
cd /usr/realtime*/testsuite/kern/latency; ./run
/usr/realtime-2.6.12-magma/testsuite/kern/latency$ ./run

in any case the 'lat max' is hovering around 11000ns, with and average of 470ns or so. ovl max is 12000ns.

According to the wiki, an ovl max less than 15000-20000 ns should yield nice results