Old computer... Use it or ditch it?

Hi everybody!

This is my first post, so let me first introduce myself...

Since quite some time I am using other people CNC's (routers) and I eventually decided to get my own...

I am currently looking at the electronic/driver part. Nothing fancy: 3/4 axes, spindle control, ready for expansions (MPG, ...).
The only thing is that I would like to be able to 'pulse' relatively fast (100-200KHz) which rules out parallel port solutions.
I m not in favour of USB, so there is not much left over...

I looked at boards like SmoothStep or Pokeys57CNC, but I am a bit reluctant as they only run with Mach3/4 and I would have to buy a Windows PC which is not my favorite choice

Although Linux is my platform of choice I initially did not considered LinuxCNC as in my mind it was parallel port only and I didn't want to go there ...
... until I discovered the Mesa boards

So I eventually set my mind on a setup based on a 5i25/6i25 + 7i76 (or a 7i76E).
I browsed the forum for recommended computer hardware, but before buying anything I wanted to check if I could use my 10 year old machine running Debian.

It is an ASUS M2N4-SLI board (AMD Athlon 64 2GHz dual core) with 3GB or RAM and a NVIDIA GeForce 7300GT (Looks like it's not recommended )

I dowloaded the latest iso of LinuxCNC (2.7.3 / Wheezy) and started checking latency (Linux 3.4.9-rtai-686-pae).
The graphic card is using the 'nouveau' driver.
It went well for some time (2 gears and watching youtube videos), but then from time to time I got a peak up to 75ms



As one can see in the graph, it is relatively constrained, but we do have values "out of range". I tested quite long time and it never go beyond 75ms...

I have no clue from where these glitches are coming from, I can't find a pattern -- It can run half an hour under 15ms, then get a 75ms peak.
it does not seems to be network related (no peaks when I stress the net).
I can open more than 10 'gears' and they all work fine.
No latency increase during video playback...

I have disabled what I could in the BIOS (but there is not a lot to disable...)

I tried to run with isolcpus=1, but the machine becomes too slow (you can't even play a video)

Next things I tried were the older kernels
- Ubuntu 8.04 with 2.6.24 -16-rtai (not smp): gears are slow (probably due to the old free nvidia drivers) and after a while I got the 75ms glitch as well... (just running gears)
- Ubuntu 10.04 with 2.6.32-rtai SMP and the 'nouveau' graphic drivers; again back to 75ms after 30 minutes

Note that I did all the tests from the LinuxCNC live dvds, I can't install anything on this machine right now, so I am limited in what I can try (e.g. nvidia proprietary drivers, other kernels...)

So this leaves me with a couple of questions...

• Should i ditch this old desktop and buy a something else?
• Any tips / test I could do?
• If there are no improvement would this latency be good enough for the Mesa external pulse engine?

Thank you in advance!

It is good enough for use with Mesa cards.

Do NOT install nvidia drivers, latency will get worse and you may have openGL problems.

regards

EDIT: I assumed you have your ms and us mixed up. No-one gets 75ms jitter normally.

Thank you for the quick feedback.

And yes I meant micros, not millis

I'll get a new disk for this machine, do a real install and run some additional tests to confirm the latency and see if I can make it better, but I understand it is good enough for use with a Mesa board.

I still have to bite the bullet on which card I'll get -- 5i25, 6i25 or a 7i76E.

I like the idea of the Ethernet board but I understand as well that the PCI ones have been there since a longer time, are widely used and well supported. Also PCI gives a more 'direct' connection than Ethernet which will add latency. Also my old mobo has only one Ethernet port which is again not so good.
I have both PCI and PCIe slots so it does not matter too much for the 5i25 / 6i25 choice, but should I have to go to a more recent computer, PCIe looks a better choice.
Full size / Low profile: does not matter, it is just the bracket that can be changed if the case changes...

Just for the record, I tested about all the combinations on local disk (instead of the live cd) with no real improvement.

Eventually I stripped the machine to the bare minimum (no floppy, cdrom, ...) and replaced the 13 year old IDE disks with an SSD.

With Jessie and the latest kernel it is looking now a bit better:


(Output after running 3 glxgears and playing Youtube channels for a bit more than 22hours)

In the meantime my 6i25 board arrived, so I'll proceed to the next step: (try to) get the real thing up and running!

Yes, I understand that -- I just wanted to be in the best possible shape at start, and I retested the the system in it's "final" hardware configuration.

I installed the 6i25 in the computer last night -- which gave me some headache as X didn't want to start anymore; but that's all fixed now -- so I'll try to connect my steppers over the week-end and see how it goes.

(It is a new build, I am currently gathering all parts, so we still have plenty of time before seeing chips flying through the shop )