run-time OS need of memory

[Joel Sherrill]

Francesco Poletti wrote:
> 
> Hy all,
> I'm using RTEMS with an Arm6 core simulator and I'm asking what'is the
> real need of memory at run-time for the data of the operating system.
> Is possible to have an idea of the amount of that memory? Have someone
> else make some similar measurement. What are the result?

The answer is that it always depends upon what services you have 
configured and enabled in the application (or test) in question.

I assume you want to run the test suite.  The tests can be run
in a target with 1 MB for code, data, bss, and heap.  I believe
that until you get into the networking tests, that number should
be well below 512K.

For real applications with a focus on trimming memory, people have
fielded 68k applications with as little as 128K memory for code, data,
etc.

The quickest way to get a feel for this is to do a size on all the
test executables.  That gives you the code, data, and bss requirements.
Then it is just a matter of heap and RTEMS workspace.  

Many of the BSPs used to (and may still)
hardcode the heap size to 64K.  Not enough for networking but plenty
for the tests and the applications those boards were being used for.

The test spsize can give you the formula for RTEMS workspace usage.

> Thanks to all in advance Francesco.

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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