Real-time UNIX(registered trademark of AT&T)

[rracine@AJPO.SEI.CMU.EDU]

Fred Hosch asks:
>I would appreciate any information on developing real-time systems with
>Ada in a unix environment. Thanks.

It all depends on what you call real-time.  MASSCOMP guarantees an interrupt
response time of 8 milliseconds.  For some applications, that is fine.  For
an airplane control system trying to run every 10 milliseconds, that is
considerably too much overhead.  And considering the number of people who
do not use Ada tasking because they cannot afford 100 microseconds for a
rendezvous, 8 milliseconds is not likely to be acceptable.

This is, by the way, not an Ada issue.  General purpose operating systems
have too much to do to be able to give users quick response.  

The IEEE POSIX standard folks are working on a "real-time" interface, based
on work by AT&T, MASSCOMP and others.  Getting implementations which
deliver the performance allowed by the interface might take a while, though.

Roger Racine
C.S. Draper Laboratory
rracine@ajpo.sei.cmu.edu
(617) 258-2489