Re: LinuxCNC laptops

I used to work at Intel, and I still know people who work at Intel, and I
can tell you this kind of problem continues to get worse. The good news is,
with higher processor speeds the system management tasks take less time. The
bad news is, laptop makers continue to get more and more proprietary in
their designs. You may have noticed that laptops almost always ship with a
"special" version of Windows. I once had a Compaq laptop that wouldn't work
any more if you formatted the hard drive. (Of course they did that with
their desktops as well, but we all know what happened to Compaq.) Add to
that VMX from Intel and SVM from AMD, and the target keeps moving. Bottom
line is you never know until you try, and laptops are most likely to have
problems with any real-time application because they were not made for that.
Not that PCs were made for that either. The days when all PCs conformed to
the IBM PC/AT specification are long gone.
--
Phil Mattison
http://www.ohmikron.com/
Motors::Drivers::Controllers::Software

----- Original Message -----
From: Stephen Wille Padnos <spadnos@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, March 03, 2008 8:18 PM
Subject: Re: [CAD_CAM_EDM_DRO] LinuxCNC laptops


> Hi there.
>
> (I'm not sure if you're the same person who asked this question on the
> EMC-users list, but just in case you're not, here goes ... )
>
> Laptops are particularly susceptible to having problems due to power
> management. Intel built a special mode into their processors, starting
> somewhere in the 386/486 release cycle. It's called SMM or System
> Management Mode. The SMI interrupt is what puts the processor into this
> mode, and that interrupt can't be turned off. (even though some
> chipsets may allow it to be turned off, this is actually out of spec for
> the chip since thermal management is done in this mode, among other
things)
>
> So here's the problem: every 64 seconds, and whenever a "system
> management event" occurs, the processor will stop whatever it's doing,
> and go off to take care of "system-y things". This can take several
> hundred milliseconds to complete. I'm not sure why it's so slow,
> considering that 300ms is about a billion cycles these days, but that's
> the kind of latency we've measured. If this happens when you're trying
> to output steps at a rate of 15 KHz, the step stream will suddenly stop
> (no deceleration) and then start up again a while later (with no
> acceleration), which is likely to cause the motors to stall, or at least
> to lose steps.
>
> This isn't a problem with EMC2 specifically, it should happen to other
> programs as well, including Mach3 (due to Windows), and possibly even
> TurboCNC (since SMI is supposed to be enabled by default). Sometimes
> you can get acceptable performance by tweaking the BIOS and testing (a
> lot). I don't know of any solutions that "just work", especially for
> many different CPUs and chipsets. If anyone has a good, general
> solution (for Windows or for Linux), I'd like to hear about it so we can
> incorporate it into EMC2.
>
> There are sometimes other problems with latops as well, such as
> insufficient drive strength from the parallel port, or no parallel port
> at all :)
>
> - Steve
>
> marcin_ose wrote:
>
> >Dear Group,
> >
> >Can you suggest what brands of laptops have good compatibility with
> >LinuxCNC, and what distribution of Linux you would recommend? I'm
> >looking for a laptop, and want to make sure that it will work well
> >with LinuxCAD for an CNC acetylene torch table that we're building.
> >
> >Thanks,
> >
> >Marcin