Do I have a strange latency issue?

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27 May 2017 14:38 #93709 by TrialByFire01
Possible Latency spike issues

The problem I am having is trying to determine my max latency (besides being a noob)
When I use either the integrated graphics or the ATI card and absolutely nothing running but whatever runs at boot with RAM in non-interleaved mode and the Latency-Test going my Max Latency starts out at (1ms)996100, 1600 and (25us) 27591, 2752 they both slowly crawl up about 10-15% the (25us) reading crawls up a little more than the (1ms) until about 1800 and 2300 respectively over a period of 10-15 minutes sometimes longer, then all of the sudden it jumps to (1ms) 35079 and (25us) 39598 and it will grow slightly over an hour or so. I can reset the Latency-test and it starts all over with same spike after 10-15 min. I have better performance with the ATI card installed with driver that comes with the Live CD install and I can run at least 6 instances of glxgears with little effect each using about2% memory according to system monitor but I still have the same problem...... if it is a problem?. Also I have not connected to the stepper controller and motors at all.

From what I have read this doesn't match the typical latency spike profile,
The PC I am using is:
Dell Poweredge SC420 with an Intel P4 2.8Ghz 800Mg FSB
speedstep is not an option in this limited bios
2 512k DDR2 ECC matched pair and 1 stick of 256k DDR2
Integrated Intel Graphics and or an ATI Radeon x300 graphics card
I have all power management turned off, hyper threading turned off (everything I can turn off in bios that is listed in the wiki) and I have tried both dual interleaved mode with just the 2 ECC sticks (Problem is worse in this mode) and found better performance in asymmetric mode with the all three memory sticks.
Debian Wheezy Linuxcnc 2.7 live CD installed.

I have another slower system Dell Dimension 1100 running ubuntu-10.04-linuxcnc1-i386 Emc2 2.4 and I have the same issues. But worse latency performance.
Thanks in advance for any help.
The following user(s) said Thank You: uli12us

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27 May 2017 15:46 #93710 by uli12us
Do you use, w-lan instead of cable lan. I have seen only that is some 12 times slower as with cable.

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27 May 2017 22:29 #93723 by tommylight
That is in most cases normal, and the under 40.000 latency is ok for almost everything you intend to do. That is a server, right? Besides making to much noise, they are very nice.
If you intend on using software step generation and parallel port, it is still very usable, just put 50.000 on stepconf when asked for it.
If using Mesa cards, you are good for anything you might need as Mesa cards do not use a base thread and can reliably work with bigger latencies.
You can use the older computer as well, download and try the 10.04 linuxcnc iso, might get better latency from it.

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28 May 2017 02:05 #93737 by TrialByFire01
That is with no Ethernet connected and USB wireless dongle unplugged, I figured I needed to eliminate everything possible to chase this apparent non-issue down. thanks for the replay

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28 May 2017 02:56 #93738 by TrialByFire01
Thank you tommylight, you have no idea how happy I am to hear that I don't have a giant goose egg of a server. I'm pretty excited to finally get to the stage where I'm wiring everything up and installed the Linuxcnc. I thought I was in for more expenses, I have been chasing this for 4 or 5 days and was ready for the hammer treatment. I'm not sure about the software step generation, I haven't gotten that far yet, it took me 3 years to build my CNC machine. I will be using the parallel port to start, I'm not exactly sure what a Mesa card is but if it needs anything other than a PCI X1 or strait PCI slot I'm out of luck.The drawback to those Dell Poweredge servers is they took half the pins out of the one and only PCIe X16 slot and call it an X8, you have to cut 2 dividers out of the plug just to install a video card and run as X8. Is software step generation necessary with the Gecko G540?

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28 May 2017 11:43 #93745 by tommylight
Gecko is controlled through parallel port so you need software step generation, it can also be controlled by Mesa 5i25 PCI or 6i25 PCI-E or 7i92 ethernet.
Plenty of options.
Start with parallel make it work properly, later you can add in as you see fit.
Did you already get the 540? I had plenty of them and they are perfect for a lot of things, i just can not stand the input divider by 10, it meses up precision. They are very high quality drives anf i still use some 320 and 212 after removing the dividers.
As for latency, a lot of posts on the net tend to make a lot of noise about it but it is not. I offten use a Dell Latitude 6510 with parallel port on the docking station and despite having terible latency of over 300.000 i can use it without any issue ever, just set latency at 500.000 in the ini file. That will hugely limit the number of steps per second so i use it on slower machines but it works.
Regards,
Tom

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30 May 2017 05:48 #93827 by TrialByFire01
I already bought the G540 and It's been sitting around for a year waiting on me to get to the point I'm at right now. Would you tell me how you remove the input divider? I was an electronics tech for almost 30 years, If someone points me in the right direction I can usually get most anything done with electronics (Excluding PC's....I hate them) I had at first made my own breakout board and driver board from a design posted in the net using an A3979 as the Controller/Driver I.C. but I bought the 540 to save time. I have only completed 1 axis so far and it is untested as of yet.

How much will the precision suffer with the input divider x10? I am building this to make fairly precise parts...I hope.
I am using ACME 1/2-10 rod to drive the axis, I did this on purpose, not really to be cheap but so I could have very movement on a per revolution basis. I am fully uninformed when it comes to the quality of the ball screws available out there that are affordable in the length I need and can always add them later if needed (As you can probably tell I'm not in much of a hurry). So far I have no measurable backlash measuring with a dial indicator on each axis. I'm not too concerned with speed but I don't want to wait 3 weeks for a part either.

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30 May 2017 10:46 #93837 by tommylight
I never checked if the divider can be removed from g540, i did remove them from g320 and g212, although it was quite some time since then, but i am sure i removed them if they where installed. They vere installed on small PCB so was easy to remove them.
I did not remove them from g540, it was such a nice package thet i did not want to open it.
If using smal pitch screws, the error would be minute so do not worry about it.

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