Re: Ada.Execution_Time

[Simon Wright <simon@pushface.org>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> Your discussion of real-time scheduling using this still seems to me
> to be more in the realm of academic exercise than something
> practical. I'm sure that it works in very limited circumstances, but
> those circumstances are getting less and less likely by the year.

Sounds as if you don't agree with the !problem section of AI-00307?

The first paragraph says that measurement/estimation is important, and
that measurement is difficult [actually, I don't see this; _estimation_
is hard, sure, what with pipelining, caches etc, but _measurement_?]

The second paragraph says that in a hard real time system you ought to
be able to monitor execution times in order to tell whether things have
gone wrong. Hence Ada.Execution_Time.Timers.

The third paragraph talks about fancy scheduling algorithms. This is the
point at which I too start to wonder whether things are getting a bit
academic; but I have no practical experience of the sort of real-time
systems under discussion. We merely have to produce the required output
within 2 ms of a program interrupt; but the world won't end if we miss
occasionally (not that we ever do), because of the rest of the system
design, which has to cope with data loss over noisy radio channels.

The last paragraphs call up the Real-Time extensions to POSIX (IEEE
1003.1d, after a lot of googling) as an indication of the intention.