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Re: Embedded/Real-Time Linux?



Another option you may want to look at is timesys/linuxRT. They don't
implement Linux as a low-priority RT task the way RTlinux/Lineo etc.
do. They add real-time scheduling to the linux kernel in a novel but
effective way. The advantages? Go and look at their site for info.
http://www.timesys.com/

I agree totally with the guy who said you should make sure you
_really_ need RT before you go that route. If you do decide that
hard deadlines are essential for your product then make sure you
do rate or deadline monotonic analysis and scheduling. Read up
about priority inversion, PI avoidance protocols and stuff -
a major headache for RT systems. Figure out a way to simulate
worst-case conditions for testing your product. Now, make
conditions even worse .. ;)

Go and browse comp.realtime for more info.

Joel Who? I've been working in RT/embedded stuff in this country
for over 15 years, and I've never heard of the guy .. ;)

>
> ------------------------------
>
> From: "Gilad Ben-Yossef" <gilad@benyossef.com>
> Subject: RE: Embedded / Real-Time Linux ?
> Date: Mon, 13 Aug 2001 12:31:56 +0200
>
> Hi,
>
> > We need to port a software stack from a "standard" RTOS to embedded =
> Linux.
> > As we're not familiar with the Linux world in general and in=20
> > particular with
> > its embedded/RT variants I would appreciate any help/feedback.
> >=20
> > * What are the leading RT Linux implementations ?
> > * What should be the main considerations when choosing an =
> implementation ?
> > * Any known / common pitfalls ?
> > * Does any of the commercial distributions (of RT Linux) have a=20
> > local rep in
> > Israel / Tech Support / Consulting ...
> > * Are there any local consultants familiar with RT Linux ?
> > * Is anyone using embedded/RT Linux over here ?
>
> First, consider well wehther you needs are an embedded OS, or true hard =
> real time OS.
> If missing a bit once in a long while won't kill anyone, blow up the =
> product or otherwise be totally unaccptable then you don't need an hard =
> real time OS, just a good embedded one. (No, routers are not hard real =
> time devices. Yes, I do know what I'm taqlking about ;-)
>
> It makes a very big difference and there is a lot of mix up in this =
> field. There are a lot of people who are sure that they need an RTOS =
> when all they really need is a good embbeded system with good =
> performace. Linux excels as an embedded system, but the most common RT =
> solution for it seems to be running Linux as a thread under another real =
> time kernel (there are exceptions).
>
> If what you really need is an embedded OS (but with good perfomance), =
> then my recomendation would be either of the following:
> 1. "Role your own" - get a Linux pro to make you a custom Linux =
> distribution, a la the Linux Router Project.
> 2. Buy this service from Monte Vista, Lineo or the like (my preference =
> would be Monte Vista, but your mileage may vary).
>
> If you need true hard real time OS, don't use Linux. But most chanes are =
> that you really don't.
>
> Whatever you do, make sure you understand the full legal implications of =
> the specific terms under which Linux is licensed (GPL v2 + the Linus =
> allowance for closed binary kernel modules) as they are going to have =
> direct effect on your design.
>
> If you're looking for a good consultant in this territory then Joel =
> Issacson is your man (send me a private email if you want his phone =
> number). I don't think there is an embdeed or real time  project going =
> on in Israel without this guy... ;-)
>
> I've not only been using Linux as an embedded platform for fast wire =
> speed network proccesing applications as part of my work, I'm also aware =
> of at least 4 other companies in Isreal who do (I consulted for some). =
> No doubt more exists.
>
> I'd be happy to answer any questions you might have on the subject. Good =
> luck!
>
> > Thanks in advance,
> > Gal Nachum.
> >=20
> > p.s. how 'bout adding a RT section to the FAQ ...
>
> That's a cool idea...=20
>
> Gilad.

-- Jeremy Hoyland
jeremy.hoyland@bigfoot.com


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