Consider FAA AC 20-148 - Reusable Software Components in RTEMS Software Engineering manual

[Sebastian Huber]

Review of the Software Requirements Engineering chapter for the RTEMS Software Engineering manual suggested that we should take the ​FAA AC 20-148 - Reusable Software Components into account:

​https://lists.rtems.org/pipermail/devel/2019-November/056027.html

    +Resources and Performance
    +-------------------------
    +
    +Normally, resource and performance requirements are formulated like this:
    +
    +* The resource U shall need less than V storage units.
    +
    +* The operation Y shall complete within X time units.
    +
    +Such statements are difficult to make for a software product like RTEMS which
    +runs on many different target platforms in various configurations.  So, the
    +performance requirements of RTEMS shall be stated in terms of benchmarks.  The
    +benchmarks are run on the project-specific target platform and configuration.
    +The results obtained by the benchmark runs are reported in a human readable
    +presentation.  The application designer can then use the benchmark results to
    +determine if its system performance requirements are met.  The benchmarks shall
    +be executed under different environment conditions, e.g. varying cache states
    +(dirty, empty, valid) and system bus load generated by other processors.  The
    +application designer shall have the ability to add additional environment
    +conditions, e.g. system bus load by DMA engines or different system bus
    +arbitration schemes.
    +
    +To catch resource and performance regressions via test suite runs there shall be
    +a means to specify threshold values for the measured quantities.  The threshold
    +values should be provided for each validation platform.  How this can be done
    +and if the threshold values are maintained by the RTEMS Project is subject to
    +discussion.

We focused on big-O and whether methods were constant time, bounded, or O(n)
when designing. Perhaps the focus could be there. But this is a design goal for all
of RTEMS and something we would document. Nothing to do except a general
design goal.

This section also sounds like part of what is required by a systems integrator
when leveraging what the FAA calls a Reusable Software Component:

https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22207 

You get credit for what's common and have to fill in details for your system.