Microcontroller Vs Microprocessor for RTOS

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Dear all,
I am just curious to know why almost all commercial popular RTOS like
RTLINUX,Vxworks work mainly on Micro processor instead of
Microcontrollers?
AFAIK,I have seen Vxworks work on Boards like Intel x86,powerpc,ARM and
all mentioned processor boards instead of real microcontrollers like
8051,68HC series from motorola and so.
Why do RTOS prefer microprocessors as compared to microcontrollers?

Though I know few RTOS like RTX-51 which runs exclusively only on 8051
microcontrollers,still such things are not so common in embedded world.

I would like to hear some real facts behind this decision instead of
starting a religious war of using microcontrollers or microprocessors
with RTOS...

Regards,
s.subbarayan


Re: Microcontroller Vs Microprocessor for RTOS
s snipped-for-privacy@rediffmail.com wrote :

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are you a sales person ? a manager (brr) ?
those are basics - you DONT NEED an OS on something with 128 bytes of
ram, you need every byte of resources. RTOS is a luxury


Pozdrawiam.
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Re: Microcontroller Vs Microprocessor for RTOS
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You mean "heavily advertised".  Those two, in particular, are huge.  The
last time I checked VxWorks wasn't even available for anything less than
a 32-bit processor.  There are smaller micro kernels out there made for
8- and 16-bit processors (MicroC/OS is notable).

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Because the RTOS takes chip resources to run, and microprocessors
generally have more resources to spend.  Most significantly when you do
a task swap you need to save the task's stack frame so you need storage
for as many stack frames as you have separate tasks.  This can suck up
very large amounts of memory very quickly.

Also, the benefits of an RTOS diminish as the application gets small,
and microcontrollers are more likely to have small applications.  For a
small enough application you'll spend more time dinking with the RTOS to
get it up and running than you'll save by having it there.

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Hope springs eternal.
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Tim Wescott
Wescott Design Services
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Re: Microcontroller Vs Microprocessor for RTOS

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I don't think they make such difference. Some companies even differ
between microcontroller, embedded microprocessor and microprocessor.

For an (RT)OS it is only interressting to know which architecture the
CPU has, is it 8,16,32 or more bits, does it have an MMU or FPU etc.

Esp. for VxWorks I know that it runs also on ARM base microcontrollers
(taking the definition, that a microcontroller is an CPU + peripherals
on the same chip).

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42Bastian
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Re: Microcontroller Vs Microprocessor for RTOS
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What is _your_ definition of a microcontroller ? Registersize ?

Mine is: A microntroller is a cpu + periperals on the same chip.

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Ouch, do you want to start another RTOS or not thread :-))

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But it seems to.
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42Bastian
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Re: Microcontroller Vs Microprocessor for RTOS
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Or rather a bragging session ?


Re: Microcontroller Vs Microprocessor for RTOS



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One Word "OVERHEAD"



Re: Microcontroller Vs Microprocessor for RTOS
Dear Subbu,

I think it may be this way if you are going for a specific applications
then the need for a specific controller comes into picture and then
they go for microcontrollers,

Usually an OS will be very generic and they operate on a generic
devices with so that the user will have a more flexibility for there
application but if you go for a microcontroller the devices on chip and
the controller will be very specific and the same code which is written
on the controller will have less portable options ,but if you consider
a pentium family for an example,if you have device driver for one
device on P3 the same code can be run on the P4 also.

Please let me know if i am wrong .
Thanks and Regard
Prashanth B.S.


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