RTEMS Executive vs. Kernel

Sebastian Huber sebastian.huber at embedded-brains.de
Fri Jan 25 13:03:49 UTC 2019

On 24/01/2019 00:24, Joel Sherrill wrote:
> On Wed, Jan 23, 2019 at 2:01 AM Sebastian Huber 
> <sebastian.huber at embedded-brains.de 
> <mailto:sebastian.huber at embedded-brains.de>> wrote:
>     On 23/01/2019 08:11, Chris Johns wrote:
>     > On 23/1/19 5:50 pm, Sebastian Huber wrote:
>     >> On 22/01/2019 23:42, Chris Johns wrote:
>     >>> On 23/1/19 5:34 am, Joel Sherrill wrote:
>     >>>> I don't object.
>     >>> Is executive the right abstraction? Both terms are an
>     abstraction because we
>     >>> have a single address space and literal or formal
>     interpretation breaks down. I
>     >>> see the physical separation as an implementation detail.
>     >> Real-Time Executive for Multiprocessor Systems or RTEMS already
>     has executive in
>     >> its name.
>     > The name has evolved over time.
> The M had two meanings before Multiprocessor. That's the only change. 
> We shall NOT
> discuss the previous two since those were poor choices that biased folks.
> I found the original published paper on RTEMS. It was presented in 
> August 1990
> and the text version is at:
> https://archive.org/stream/DTIC_ADA247043/DTIC_ADA247043_djvu.txt
> It is clear there that kernel and executive were considered equivalent 
> terms.
> It is also clear that operating system is used about as many times as 
> either
> term. I did not re-read the paper to see if we used executive/kernel 
> to refer
> to a core set of services and OS to refer to a larger collection.
> https://en.wikipedia.org/wiki/Kernel_(operating_system) is an 
> interesting read.
> Kernel is a valid term for us to use per that. A couple of quotes from 
> the early
> part of that ignoring the IO devices mentioned. This is the first 
> sentence.
> "The kernel is a computer program that is the core of a computer's 
> operating system,
> with complete control over everything in the system.[1] On most 
> systems, it is one of the
> first programs loaded on start-up (after the bootloader). "
> The above matches my stated view that there is a core set of services 
> that support
> others. The collective is the operating system. For the purposes of 
> this discussion,
> the rtems.git repo unfortunately contains the kernel and some OS 
> services. So the
> repo is not purely the kernel layer. It is the kernel plus core 
> services and libraries.
> "The critical code of the kernel is usually loaded into a separate 
> area of memory,
> which is protected from access by application programs or other, less 
> critical parts
> of the operating system. "
> The key point of the above sentence is "usually". This is in deference 
> to UNIX
> and Windows which do have separation. The kernel is a logical 
> abstraction which
> may have the property of separation.

This wikipedia article clearly talks about kernels that use protection 
mechanisms and system calls.

Apart from that, you all seem to favour "kernel" instead of "executive".

While searching on the web I found a PDF of the Real-Time Executive for 
Missile Systems C Application User's Guild.


It doesn't look that much different to the current Classic API guide.

Sebastian Huber, embedded brains GmbH

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