LinuxCNC on dell 1520 laptop

Hello everyone,

Long time lurker, first time poster!

I'm hoping that somebody here might be able to help me with an issue I've been encountering with trying to run LinuxCNC on my dell 1520.

Firstly, I know that laptops aren't the best at running linux CNC
Secondly, I know that the 1520 hasn't got a par port but I know of an express card that allows for a full hardware par port (not printer only)
Thirdly, I'm quite new to linux but I'm not new to researching things and finding out for myself but I've reached my limits

So the machine itself is a 2ghz core 2 duo with 4gb ram and 840m graphics.

I have installed ubuntu 10.04 from the latest live CD and have selected the recommended nvidia drivers.

This is the problem, when running the Linux latency test I got a whopping maximum jitter on the base 25uS thread of over 300,000ns

To combat this I have:

Applied the SMI Fix
Applied the isoscpus=1 fix to grub
Applied the idle=poll fix to grub

There is next to nothing I can do in the Bios because dell don't allow access to anything.

Now, after a fresh boot, opening firefox and a glxgears window I'm now looking at 21,330uS jitter which is a vast improvement yes?

However, if I run the Kernel latency test in usr/kernel#/testsuite/kern/latency I get this.
TH| lat min| ovl min| lat avg| lat max| ovl max| overruns
RTD| -1660| -1660| -1470| 113453| 168471| 42
RTD| -1649| -1660| -1456| 99547| 168471| 43
RTD| -1650| -1660| -1462| 77172| 168471| 43
RTD| -1660| -1660| -1436| 185660| 185660| 45
RTD| -1660| -1660| -1468| 131408| 185660| 46
RTD| -1659| -1660| -1439| 137937| 185660| 48

This is now where I become really stuck because the latency in linuxcnc hal test is reasonable but in the kernel it's terrible and I'm getting overruns of which I have no idea what they are.

Any ideas?

Hi

Firstly, I know that laptops aren't the best at running linux CNC

That is an understatement
The have rightly got a bad reputation, it is because of all the power saving, temperature monitoring, battery monitoring etc. that goes on.
If the Dell BIOS does not give you many options and you can't turn things off, you are unlikely to have much success.

I have installed ubuntu 10.04 from the latest live CD and have selected the recommended nvidia drivers.

Recommended by whom?
The only driver you are likely to have any sucess with is the nouveau driver.
Any of the nvidea proprietary drivers are likely to push latency way up and may even be totally incompatible with the implementation of openGL used by Axis

... I know that the 1520 hasn't got a par port but I know of an express card that allows for a full hardware par port (not printer only)

Quite honestly you would be better spending that money on a ex-corporate P4 from ebay, than trying to get a computer inherently unsuited to running Linuxcnc to work
wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test

If you want a more modern board then look at the Intel Atom based ones, but the PSU, DVD, memory HDD etc will bring the price up.

regards

Hello ArcEye,

Thanks for the response.

I'm aware that while no idea, there is usually a way of working around the laptops issues.

The dialog box Nvidia drivers appeared on first boot as an option for restricted drivers or something. There were 2 options for nvidia drivers and a recommended one and I selected the recommended one.

I have no knowledge of a nouveau driver.

I actually have an L295 all in one PC which I'm using at the minute which is quite successful and gets fantastic latency results. It is however somewhat bulky and I'm limited on space and I have one too many computers and so was hoping to repurpose the laptop and flog the L295 rather than the laptop which is newer and better.

Hi

The dialog box Nvidia drivers appeared on first boot as an option for restricted drivers or something. There were 2 options for nvidia drivers and a recommended one and I selected the recommended one.

I have no knowledge of a nouveau driver.

Sounds like you have installed the proprietary nvidia drivers.

You need to remove them and install the open-source driver, should be nouveau on 10.04 I think,
certainly is on Debian.

This covers it and there are plenty more similar.
askubuntu.com/questions/12937/remove-nvi...d-go-back-to-nouveau

Only then will you be able to eliminate the video driver from the equation and get a base latency figure

regards

Cheers for that. Not being much of a linux user, I wasn't aware that the drivers made that much of a difference.

I just expect that newer drivers are a good thing!

So, my current state of play is:

Applied the SMI Fix
Applied the isoscpus=1 fix to grub
Applied the idle=poll fix to grub
Removed Nvidia drivers and reverted to nouveau

I now have 4 GLX gears running and the single CPU core running at 100% and getting a jitter of ~16000 in the LinuxCNC hal test

It would seem that it has improved considerably.

I did suspect the nvidia drivers because everytime I opened a GLXgears up with the latency test running, it suddenly jumped to over 400,000.

EDIT: Just opened 2 more glxgears and the 6th one is starting to struggle but no increase in the jitter.

Would this be considered acceptable?

Hi

Yes 16K is perfectly acceptable for software step generation.

See what stepgen gives you for base thread figure, taking into account your driver timings etc.
You will probably be able to tune it down from there

Just make sure you do not use too high micro-stepping, anything over 4x is a waste of pulses in the name of 'smoothness' to my mind, if you are not using hardware generation.

regards

Sounds like a plan then. I'll invest in the little express card parallel adapter at some point then as it's supposed to be a full parallel card.
I would much rather use the laptop if I can as I can simply unplug and disconnect it when I'm finished and hide it away, get back some valuable space!

express parallel adapter on ebay

I haven't even mentioned the machine I'm using!

It's a zen tool works style machine but from china, 200x200. It came as a box of bits, well it came in a box with most of the bits. Had to fab up the missing bits on my DIY machine. The Spindle was also an old servo motor with the servo removed and replaced with an ER11 chuck. It had clearly been crashed as the fan end of the motor was originally the drive end and was also bent.

I'm using 1/8 micro stepping with fast decay and 1.7A motors at 24V on an M8 thread with a red TB6560V2 board which has been a little workhorse and so cheap.

The spindle is of my own flavour, brushless motor with ER11 extension chuck currently but due to be replaced with another custom spindle using a DC motor and U pulley system I machined for higher speed milling.

Well, I figured it was finally time to gather up the courage and splurge out on the £18 for the parallel express card for my dell 1520.

I installed it, found the address, imported my old config file from my old PC, changed the address to suit, updated the jitter period from 8000ns to 16000ns and voila, my laptop is now working a treat with my CNC machine, exactly how the old computer used to run.

The extra jitter isn't a massive problem because there's still loads of leeway left on the timing.

All in all, I'm impressed. I'll run a few PCB's circuits through the machine later before I fully endorse it, see how it gets on but so far it's a pretty good impression!