[taiden]

I have Linuxcnc live CD with Ubuntu v10.04 running just fine. Latency is 8k/9k with the CPU at full load and doing all sorts of other things.

But when the case fan turns on, at the moment of switching, and ONLY at the instant it switches, the jitter goes up to about 50k/50k. When the fan is running, back to 8k/9k. At that exact instant when the fan turns off, back to 50k/50k max. After that, 8k/9k again.

Is there any way to fix this?

When I run LinuxCNC for a while the fan never kicks on. Will this be an issue? It's the only thing that seems to be an issue in this otherwise fantastic computer I've cobbled together from various machines people gave me.

[SaskFab]

You didn't mention what model of mother-board you are using but have a look through the bios settings to see if you can set that fan to run continuously instead of cycling on and off. If that's not possible, power that fan from a point that is always live and hopefully then the temp will never rise high enough to cross the threshold of the monitoring circuit that is interrupting the CPU/board/whatever and causing your spike in latency.

Marv

[taiden]

Hi Marv,

I have two computers at my disposal. One mobo is just whatever comes with the HP pavilion a330n. It has onboard nvidia graphics. This is the one I am trying to use as it gets better results than my retired gaming PC which has a geforce 4 ti 4600 agp card which spikes every now and then. The issue with the HP is the bios is total dummy mode. All you can do is change boot sequence and disable onboard items.

[SaskFab]

Hi Taiden,

I was afraid it might have a bios like that. Very common on the OEM type boxes.

It looks like your only option is to power the fan(s) directly from the 12v supply so that the onboard temp monitoring circuitry never sees a temp high enough to make it interrupt the system while it switches on the fan(s)

As I'm sure you know, there are adapters available to attach fan connectors to the standard molex drive connectors if you don't feel like soldering/splicing. I would definitely give this a try since the system seems good in all other respects.

Marv

[taiden]

Hey Marv, I have something else I want to run by you.

When I test 10.04 on the live CD I get the numbers listed above. When I do an install and I test again (no updates and NOT using nvidia drivers) I get spikes up to 10,000k. Quite frustrating.

Thanks,
Luke

[taiden]

Hey Marv,

I'm getting kind of frustrated. I've been playing around with these computers for probably 12 hours over the last two days. I have two computers I've been trying to combine into a good emc2 machine.

My machine right now will pull 8k/9k off the Live CD no matter what (except for the case fan). When I install it onto the harddrive I get 6k/7k unless I open a program that has not been opened yet then it goes to 1,000k/1,000k. Anytime I open a new window now it goes up to 50k/67k. I'm really quite frustrated at this point, because it seems to be all stuff that is completely illogical and out of my control. Is there any way to test latency while EMC2 is running? It seems to me that would be the only real test since I will not be using the computer for anything else while it's cutting.

Any help would be very much appreciated

[taiden]

Alright well I would post on the LinuxCNC forums but it wont allow me to register. So I'm hoping to get more help here.

If I get my CPU loaded 100% and have glxgears running and moving windows around it does not go above 13k now that I'm using the vesa drivers.

However, if I open a program that has not yet been opened since startup (not in cache?) it will spike to 8,000,000 ns and then go away. I calculated that at full speed this will make me lose about 40 full steps which is quite a lot.

But I cannot test latency while emc2 is running which is really the only thing that matters since this is a dedicated machine and I wont be using anything else while it's cutting.

Is this acceptable? Or do I need to look for yet another (third) computer.