typical RTEMS system HW?

[Joel Sherrill]

On Thu, Jul 8, 2021 at 3:11 AM Shiro <rt9f.3141 at gmail.com> wrote:
>
> Hello,
>
> I’m new to RTEMS but very much like its features.  I’m wonder what HW (MCU/MPU and memory size) RTEMS is typical used on.  Anyone care to share a bit of details?
>

Well I held back hoping more people on the using side would answer.
This is my perspective from the long-term developer view.

Most users are on 32-bit platforms. There have been 64-bit ports for a
long time but most people aren't using them.

There are a lot of users from the space community who tend to be on
hardened hardware. This SPARC LEON family is probably the most
commonly used there. In the early days of the LEON predecessor
(ERC32), I would say 1-4 MB was quite common for RAM. Other CPU
architectures have been used in RTEMS space-based systems like
PowerPC, Coldfire, MIPS, and ARM.

There are also a lot of users in the EPICS (Experimental Physics and
Industrial Control System) community which is commonly used in high
energy physics, astronomy, and other big science equipment. I would
tend to put a lot of those users on VME and CompactPCI boards with the
PowerPC and x86 being common. They may still use some of their old
VME m68040 boards or at least we haven't dropped support for them.
These mostly tend to have 4-16 MB RAM.

There are also a lot of commercial users and currently I think a lot
of those are on ARM platforms (STM, Xilinx, NXP, etc) with RISC-V
coming on strong. There are users on other architectures but I think
the bulk are there now. PowerPC users seem to be realizing they are on
the tail end of the lifecycle and need to look forward to a
transition.

RTEMS has been ported to 16-bit CPUs but there are none currently in the tree.

You can certainly have an RTEMS application which fits into a small
amount of Flash but as you add capabilities, you tend to pick up code
and data space requirements. The earliest RTEMS systems would be big
if they had 1-4 MB total Flash and RAM but that's considered small
these days in general. I recall one m68k based system that has 96K
total code and data space. The legacy network stack could easily run
on 1 MB RAM. Now libbsd generally has more features and takes more
memory. It may be able to be trimmed down but no one has invested the
time. lwIP would be a better alternative in those cases.

If you need a lot of features, the footprint naturally grows. If you
are on a small target board, some tests won't fit. For example, some
of the file system tests assume a 1MB RAM disk. If you don't have the
space, you just don't.

I still think that a large RTEMS system is on the smallest end of
Linux systems.

Not sure this gives specific answers but that's my impression.

--joel

> Thanks,
> Shiro
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