Dell Dimension C521 candidate or crap?

I couldn't find a search function in this forum. Maybe I missed it and there is reference to this particular machine?

Anyhow, I got a hold of an old Dell Dimension C521 with an AMD Sempron 3400+ processor running Windows XP at the right price: free, and followed the instructions for a new installation of Ubuntu 10.04 with LinuxCNC v2.5. I had to install a utility in XP to be able to mount the ISO. Where I am now is the HAL latency test. The Max Jitter is pretty poor: Servo thread - 225030, Base thread - 229913.

So should I abandon this machine and look for another or is there some amount of tweaking I can do to get to acceptable numbers? I did come across an entry in the cnczone forum from someone running Linux 2.6.32-122-rtai Ubuntu 10.04 (linuxcnc.org) on an AMD Sempron 2800+ (2GHz) so I'm wondering if I do have solvable issues?

Uninstalled 10.04 and installed 8.04. I see virtually the same numbers: 218917 and 237675. Both times, I installed from Windows XP and then booted into Ubuntu. Is there some other way?

I guess I'm wondering if this hardware is known to be bad for latency with no chance of improvement or known to be good, or just somewhere in between with a chance of making it better?

BigJohnT wrote:

There is a list of motherboards and the latency they have here

wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test

I didn't see your board.... is it more than one core? If so try some of the things on that page.

Does it spike right away or after some interval? I've seen a MB that spiked when you started the latency test and if reset the spike never happened again.

John

As far as I can tell it is a single core. It spikes after a second or two. After a reset it spikes again pretty quickly.

Hi

If you look at the FAQs on latency here
www.linuxcnc.org/index.php/english/forum...-the-latency-problem
www.linuxcnc.org/index.php/english/forum...me-latency-solutions
you will get an overview of the problem and some possible solutions.

It is unlikely to be SMI, a) because it has an AMD processor and thus unlikely to have the relevant Intel chipsets and b) because they should be regular (32 or 64 secs typically)
However run lspci -vv > lspci.txt from a terminal and attach the generated lspci.txt and we can be sure.

The FAQs show how to do a latency test from a terminal with a per second output. This will show exactly when the spikes are occurring, the dialog based one just shows a cumulative total.
Are they extremely regular, do they coincide with disc access, network activity, mouse movement, graphics repaints etc?

If they have no rhyme or reason, just happen randomly whilst the computer is just sat there doing nothing, you may have to cut your losses (as it was free there are none) and find another computer.
Don't forget to add you figures with the exact spec of the machine to the latency test wiki, then others will be warned.

regards