I don't use an RTOS because...

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I use an RTOS every day, but I was wondering why
a lot of people still don't use one?
I find it a very useful tool, but I still run into a lot
embedded engineers that don't use one, why?


Too hard?

To expensive?

I don't need one?

Never bothered to learn?

My boss said no way?






Re: I don't use an RTOS because...

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I almost always use RTOS's these days, but:

If the application is way small, or if it requires very high
reliability, then an RTOS doesn't make sense.  Otherwise its useful.

If you've never ever used an RTOS before you would pull the threshold
much higher -- learning to effectively use an RTOS is a pretty steep
curve for any one project, but it sure makes sense in the long run.

--

Tim Wescott
Wescott Design Services
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Re: I don't use an RTOS because...
On Wed, 12 Jan 2005 19:57:30 -0800, snipped-for-privacy@Rasdoc.com wrote in
comp.arch.embedded:

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Use them in some places, either commercial or custom built in house,
don't use them in others.

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An RTOS is expensive in terms of code space, RAM space, and execution
time even it has no direct monetary cost for source or run-time
licenses.  How expensive it is in those terms relative to the rest of
the application depends on a lot of factors.

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I don't use one when I don't need one.  There are two major reasons
that I can see for using an OS (RT or not) in an embedded system:

1.  It comes with a lot of drivers that you would need to build
separately, such as USB stack, TCP/IP stack, file system, etc.

2.  (RTOS only) when you need to respond to a mix of asynchronous
events with different priorities.  In this case, an RTOS with priority
based preemptive multitasking and good message passing facilities can
be a necessity.

On the other hand, something like an 8-bit micro built into a hand
control device that has to debounce user button presses and send
messages over a serial or CAN bus when they happen doesn't need one.

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Know how to use 'em, know how to make 'em for special purposes.

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My boss knows enough to leave such decisions to me, unless the
financial cost is significant.

--
Jack Klein
Home: http://JK-Technology.Com
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Re: I don't use an RTOS because...
I drive a Truck every day, but I was wondering why
a lot of people still don't use one?
I find it a very useful tool, but I still run into a lot
embedded engineers that don't use one, why?

Too hard?

To expensive?

I don't need one?

Never bothered to learn?

My boss said no way?


Simple CPUs and simple project do not need them.
Bigger project MUST use them.
Then of course there is the projects in the middle that could go either
way.

The engineer needs to decided what the project needs.  Cost , learning
curve, memory, and familiarity are all part of the equation.







Re: I don't use an RTOS because...
snipped-for-privacy@Rasdoc.com wrote :

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dont know


sometimes, everything is expensive compared do FreeBSD and Linux

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yes, but i'm lucky

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yes


I'm not that schizofrenic :))

Pozdrawiam.
--
RusH   //
 http://randki.o2.pl/profil.php?id_r35%2019
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Re: I don't use an RTOS because...
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2k flash, 128 bytes RAM, a lot to do. Nuff said?

Or requirements are simple. I don't want to use a PowerPC and 256G RAM
and a compact flash boot disk just to flash a couple of LEDs. Though it
looks better on the CV.

I use an RTOS if I need one and have the space- I even wrote one (very
simple one) once.

Paul Burke

Re: I don't use an RTOS because...

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4 k Flash, 512 byte SRAM and using message passing proprietary single stack
O/S...
Application:
    press a button ,
    send/receive commands on serial port,
    light LEDs depending on commands and button.

It is fairly easy to do this with a scheduler calling tasks implemented as
statemachines.
--
Best Regards
Ulf at atmel dot com
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Re: I don't use an RTOS because...
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They are only really usefull for big projects, especialy team efforts.

Re: I don't use an RTOS because...

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Not really. They are very useful when you need to do unrelated tasks on
a single system, or have a time sensitive control task and a number of
other tasks (human interface, setup, management) that you would like to
operate transparently while the main task goes on. Very useful in their
place, can be very expensive (in resources if not fees) out of place.

Paul Burke

Re: I don't use an RTOS because...
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In fact, one of the biggest embedded project I've worked to date
(+100,000 LOCS) is the only one in which I have not used an RTOS! That's
because it was safety-critical, and it was much cheaper to design it as
a one-task program and show its safety level this way than to use an
RTOS and show its safety level with the several tasks approach.


Re: I don't use an RTOS because...

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Hmm, I cant imagine ever using a rtos to run unrelated tasks, the inter thread
messaging system is it's only real benefit over more traditional methods. It's
true that I tend to make smaller real time systems that probable aren't
suitable for a rtos anyway, nevertheless I have no trouble running a dozen
tasks at once.

Re: I don't use an RTOS because...
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As others have said, RTOSs have their uses. But they're not a panacea.

Most of my applications are cost-sensitive and high-reliability. If I had to
choose one reason for *not* using an RTOS, it would be reliability. I'm a
big fan of the KISS principle, and I'm adept at writing complex but reliable
schedulers. Why should I spend money on something that contributes bloat and
reduces reliability?

Steve
http://www.fivetrees.com



Re: I don't use an RTOS because...
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So, you do write you C libraries yourself too ?

--
42Bastian
Do not email to snipped-for-privacy@yahoo.com, it's a spam-only account :-)
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Re: I don't use an RTOS because...

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Who said anything about C?  Real programmers can write assembly in any
language :-)

Even if you're using C, a non-hosted environment doesn't guarantee you the
existence of libc, and for lots of embedded stuff you just don't need that
sort of thing.  If you're coding to the bare metal, then the choice of
libraries is entirely up to you.  An RTOS is really just another library
choice.

--
Andrew


Re: I don't use an RTOS because...
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:-))

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That's what I meant to say :-)
Or let me put it the other way, if someone trusts libc to be reliable,
then there is no reaon why not trusting the library containing the
(RT)OS (esp. if it come in pure assembly source) ?

--
42Bastian
Do not email to snipped-for-privacy@yahoo.com, it's a spam-only account :-)
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Re: I don't use an RTOS because...
On Fri, 14 Jan 2005 14:39:19 GMT, snipped-for-privacy@yahoo.com (42Bastian

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The difference between C libraries and an RTOS is that most C library
functions can be simply documented and understood.  But giving overall
control to an RTOS requires a more thorough understanding of the
interface.  It is usually more than are series of simple function
calls.  It is more like completely understanding all the ins and outs
of the Overlapped IO operations in Win32 programming.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply
address is fake.)

Re: I don't use an RTOS because...
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If all we are talking about here is the RTOS, then the
understanding of tasks/threads, semaphores, mutexes, and
perhaps some other inter-thread communications mechanisms
is all that is required.

Yeah, it's a learning curve, but it's not *that* complex.
A worthy grok for any software practitioner.


--
Michael N. Moran           (h) 770 516 7918
5009 Old Field Ct.         (c) 678 521 5460
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Re: I don't use an RTOS because...
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See a thread I started last year re the priority inversion problems that
affected the Mars landers.

Steve
http://www.fivetrees.com



Re: I don't use an RTOS because...

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If only it were that simple.

Ian

--
Ian Bell

Re: I don't use an RTOS because...
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It is *that* "simple."


--
Michael N. Moran           (h) 770 516 7918
5009 Old Field Ct.         (c) 678 521 5460
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