Footprint of RTEMS!!!!

[Joel Sherrill <joel@OARcorp.com>]

Vivek Dua wrote:
> We intend to port it to MIPS4kC. What would be your estimation in this
> case regarding the footprint?

As Ralf said, it largely depends on your application profile.  If you
are going to use networking and POSIX, you will use more memory than
if you don't.  Also we are giving you REAL numbers not marketing
ones.  These are sizes for COMPLETE programs that do EVERYTHING.
We include BSPs, device drivers, C library, etc.  Who cares that
a specific set of functions in the RTOS is X KB.  That is meaningless.

The smallest applications range from 64K-128K on nearly
all CPU families.  This usually includes console and tick
drivers, reentrant C library and malloc support, and clean
startup and shutdown.  You can write an entire app like this.
I know of one robotic app on a 68k that said they only
had 96K and had multiple tasks.

The larger applications with networking, httpd, POSIX, etc, etc
tend to be larger with the largest network demo programs from RTEMS
tending to be about 256K-400K linked depending on the processor.

RAM usage is mostly a function of your application.  If you use
large stacks, lots of message buffers, and lots of TCP/IP buffering,
you could easily use 512K RAM.

The range is up to RTEMS.  The precise answer is up to you and
your application. :)

--joel


> Thanks for your instant reply.
> Vivek.
> 
> -----Original Message-----
> From: Ralf Corsepius [mailto:ralf_corsepius at rtems.org] 
> Sent: Friday, September 24, 2004 3:22 PM
> To: Vivek Dua
> Cc: RTEMS Users
> Subject: Re: Footprint of RTEMS!!!!
> 
> On Fri, 2004-09-24 at 11:23, Vivek Dua wrote:
> 
>>Hi all,
>>
>>I could find any answer for the below questions in the previous
> 
> mailings
> 
>>hence this question. 
>>
>>Our BU is looking into RTEMS as a possible RTOS for our product.
>>
>>Since we have strict memory constraint, I would like to know the
>>following:
>>
>>1. What is the minimum Footprint (Code + Data + BSS) possible in RTEMS
>>(bare bone RTOS) without any applications? 
> 
> It's highly architecture/target dependent and partially configurable.
> 
> The typical size of "minimal applications", in most cases somewhere in
> the order of 64k-128k.
> 
> 
>>2. Is it possible to customize the RTEMS? In other words, is it
> 
> possible
> 
>>to include only desirable components of RTOS in the final image?
> 
> Yes. To some extend this is done implicitly by the linker, to some
> extend this is configurable, to some extend this depends on your board
> setup and your applications ("Don't use printf and the size will shrink
> by several 10k").
> 
> 
>> Since
>>we do not want to include any FFS or network stack in the RTEMS build.
> 
> 
>>Would be grateful if somebody pitches in to answer this.
> 
> Download the rtems-toolchain which is known to resembles most to your
> projected target, build the sample applications for it and check the
> sizes.
> 
> Also, should you start to port RTEMS to a new architecture, consider
> contributing your code early. Some details which might appear difficult
> to understand to you might be easy for others and vice versa. ;)
> 
> Ralf
> 
> 


-- 
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
    Support Available             (256) 722-9985