LinuxSA Mailing list archives

  From: Rick Marshall <rjm@herzfeld.com.au>
  To  : Alan Kennington <akenning@dog.topology.org>
  Date: Wed, 31 Mar 1999 15:31:59 +1000

Re: Linux in real time (was More Meeting Information)

Alan Kennington wrote:

> Andrew,
>
> I probably know much less about real-time OSs than most people, but...
>
> When I talked about real-time software, I meant in the sense of
> kernel modules being able to completely take control of the CPU.
>

Realtime is generally taken as meaning the system will guarantee that a
signal (e.g. interrupt, state change, etc) can be responded to within a
nominated amount of time. e.g. on  a plane a sensor indicating a change in
air direction must be responded to in "n" milliseconds. This doesn't
preclude multitasking or require exclusive CPU usage. But it does normally
require pre-emptive process scheduling.

FWIW

Rick

> I.e. linux does not provide real-time functionality at the process
> level, but like most OSs, real-time can be achieved in device drivers
> (i.e. kernel modules).
> Of course, if you want _two_ kernel modules to achieve real-time
> functionality, then one is in trouble.
>
> Therefore I was only referring to the fact that linux is ideal for
> kernel module writing, and that the kernel can do what it likes
> with the CPU. This is a much more limited meaning of "real-time"
> than in the context of real-time OSs.
>
> Also I should mention that I was not talking about microsecond-level
> real-time. I only meant down to a few milliseconds.
> I assume that the _real_ real-time will be done on
> dedicated microcontrollers which are connected by various buses to
> the main CPU, being a sort of x86 or something.
>
> Therefore in the sorts of projects that I was talking about,
> I envisage there being a box containing a board or two, which have
> a CPU + RAM + 1 or more microcontrollers.
> Then I was asserting that linux would be good for the CPU -- but
> probably not for the _real_ real-time processors, which are the
> uC chips (e.g. microchip PIC, philips XA, coldfire etc. etc.).
>
> Cheers,
> Alan Kennington.
>
> --
> Check out the LinuxSA web pages at http://www.linuxsa.org.au/
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--
mailto:rjm@herzfeld.com.au <=>  RICK MARSHALL  <=> http://www.herzfeld.com/isl
   International Software Laboratories Pty Limited - Australia, New Zealand
     Footwear: Retail Management, Point of Sale, Wholesale, Manufacturing
    (-: All in Linux :-)   (-: On the Web :-)   (-: All in UNIBASE 5GL :-)



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