RTEMS technical information

Joel Sherrill joel.sherrill at OARcorp.com
Thu Jul 5 21:04:55 UTC 2001

"Amy Quach (TYCO)" wrote:
> Hello,
> I am currently evaluating real-time operating system for our project. I
> would like to
> find out more about RTEMS such as contact switching time, minimum kernel
> size, etc..
> Can you please tell me where can I get this information from.

ALl of this information depends on many factors.  The main one being
what CPU family/model are you interested in?  THe architecture
alone makes a lot of difference and the speed of the particular 
CPU model you are planning on using makes it even harder to
give an answer.  Greg Menke gave you an answer for a VERY slow
MIPS.  Some users are on 300+Mhz PowerPC's and see times in the
< 1 microsecond range for many RTEMS operations.

The size measurements also vary.  We like to talk in terms of
application profiles.  You may or may not use features like
the POSIX API, a filesystem, TCP/IP, etc.  RTEMS is library
based so you can easily rang from the 30K range for an executable
to the 400K range.  

The smallest currently defined application profile is a
single task which shuts down the system.  This forces you to
link in the BSP to initialize and shutdown the hardware.  This
is a more meaningful baseline.  Although a BSP can certainly
reference things unnecessarily, this size tends to be in the
40K-64K code space range.

On the 68360 and PowerPC, one can have TCP/IP with a web
server and ftp server running for around 256K code.
> Regards,
> Amy Quach
> Software Engineer
> Tyco Electronic Product Group
> Tyco Fire & Security
> Tel: (02) 9638 8226
> Fax: (02) 9638 8113

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

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