RTEMS in AMP mode

Sebastian Huber sebastian.huber at embedded-brains.de
Fri Oct 12 05:49:37 UTC 2018

On 11/10/2018 17:32, Thawra Kadeed wrote:
> Thanks a lot Sebastian for your answer.
> Actually, we are planning to run a multi-core system using a 
> network-on-chip and network interfaces as a physical interconnect 
> between cores instead of the bus interconnect. I understood that MPCI 
> by the OS maybe stay the same even if we change the RTEMS version. Is 
> that right?

Probably yes, but I guess the MPCI support is not in wide spread use 
currently. It will be definitely easier if you use the same RTEMS 
version on all nodes. One option would be to use RTEMS SMP instead.

> On the other hand, I was looking for a very old version of RTEMS and I 
> found in this site "https://git.rtems.org/rtems/tag/?h=3.5.1" a 
> version from 1996
> which is really lightweight. However, I have not seen any support for 
> ARM cortex A architecture.

The ARM Cortex-A didn't exist in 1996.

> The issue is actually that the current version of RTEMS is hard to 
> predict and analyze because it supports many features to provide high 
> performance like POSIX and others. in the real-time part, we need very 
> lightweight RTEMS excluding all other features where the RTEMS kernel 
> does not exceed 1 MB.
> So what do you recommend us? could we use the current version 
> excluding all other advantages from the RTEMs kernel where we minimize 
> the kernel as much as possible?

RTEMS is a library and it was designed so that only parts needed by the 
application end up in the executable. This improved over time, so RTEMS 
5 is probably the best RTEMS in terms of modularity. RTEMS 5 supports 
transitive priority inheritance. This makes it a bit more complex 
compared to earlier RTEMS versions. It would be possible to bring back 
the simplified priority inheritance support if there is a real need for 

If your limit is 1MiB, this all doesn't matter. This is more than enough 
for the operating system core. If you need the new network stack 
(libbsd), then you may need more (about 2MiB).

Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
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