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
>http://openfarmtech.org/index.php?title=Torch_Table
>