Re: Multiple instances of run-time sys?

[stt@henning.camb.inmet.com (Tucker Taft)]

In article <3fo5k4$su2@miranda.gmrc.gecm.com>,
R.A.L Williams <bill@valiant> wrote:
> ...
>Suppose we have a CPU (one of many in the system) which is required to
>run, say, two COTS applications, almost certainly from different
>vendors (eg. radar processing and nav. processing). Now, both of these
>are written in Ada (because we always obey the mandates don't we), but,
>quite possibly, developed using different compilers.
>
>So, what happens about the run-time systems for these applications?
>Most run-time systems for embedded applications make the following
>assumptions about their environment:
> - Their app. is the only one running on the CPU
> - They are supplying all hardware interfaces to the board, ie.
>   initialisation, interrupt dispatch etc.
>
>As I see it we have a number of alternatives:
>1. Write an operating system that provides a 'virtual machine' for
>   each app. and its run-time to run in.
>2. Find a compiler that allows multiple applications and reconfiguration
>   and then recompile all apps with this compiler.
>3. Write our own run-time system which allows the same as 2.
>
>There may be more. I don't know of anywhere, at present, where the
>technology for any of my alternatives exists.
>
>Does anyone have any suggestions?

The Distributed Systems Annex of Ada 95 is designed to allow systems to
be built out of several "partitions" working cooperatively.  
Each partition has its own run-time system; the interactions
between partitions are based on remote subprogram calls,
or on shared global data partitions.  The expectation
is that these partitions could be built by distinct compilers, and run
either together or on separate CPUs.  It remains to be seen how many
compilers will end up supporting this annex, but if it becomes widely
supported, "federated" and "distributed" systems should be relatively
easily buildable using off-the-shelf Ada 95 compilers.

>Bill Williams

-Tucker Taft   stt@inmet.com
Intermetrics, Inc.
Cambridge, MA  02138