Re: [CAD_CAM_EDM_DRO] LinuxCNC laptops

Right. I was just pointing out that the RTK takes care of other
higher level stuff that would otherwise contribute to similar
glitches.

On Mon, Mar 3, 2008 at 10:26 PM, Stephen Wille Padnos <spadnos@...> wrote:
>
>
>
>
>
>
> Michael Fagan wrote:
>
> >I don't know about this particular issue, but one of the main
> >differences between the EMC2 packaged Ubuntu version and the normal
> >Ubuntu distro is that it runs a real time kernel which is designed to
> >help prevent this sort of interruption, at least at the OS level. It
> >makes the computer slower for GUI and other tasks, but a lot better
> >for CNC controls.
> >
> >
> This issue still crops up on the realtime kernel. There are workarounds
> that work on some computers (but not others).
>
> The System Management Mode is a higher priority interrupt than any of
> the timers available to the RT system. (it's actually higher priority
> than NMI, the "non-maskable interrupt" - that's very very high priority
> :) ) A system management interrupt will halt execution of an RT task
> just as easily as a userspace task. Even if it doesn't interrupt an RT
> task, as soon as the RT system yields the CPU to the non-realtime
> processes, the SMI processing will be done, and that will delay the next
> execution of the RT tasks.
>
> Note: I haven't stuck a modern CPU on a logic analyzer to test this
> stuff - I can't afford the equipment :) If anyone has more info on the
> subject, I'm all ears.
> - Steve
>
>