Re: Timers in application

[dennison@telepath.com]

In article <080619991316219725%hopperj@macconnect.com>,
  "James E. Hopper" <hopperj@macconnect.com> wrote:
> Its been several years, but when we needed timers with a flight sim i
> was working on to synchronize the executive, we found ada constructs
> either took to much over head, or did not have sufficient accuracy.
if

In the old Ada83 days, I had similar problems. "delay until" did not
exist, and there's no way to use "delay" for the same purpose without
loosing time. There are ways to use it without *progressivly* loosing
time, but its still inaccurate by the amount of time it takes to
perform the absolute time to delta time calculation (which is not a
constant on a RISC CPU). Since it couldn't be used accuratly for
real-time scheduling anyway, there wasn't much incentive to make "delay"
itself very accurate.

Today with "delay until" around its a completly different story. Of
course you should check your verdor's listed accuracy, but it is quite
likely to be good enough for a 10Hz frequency. Using this for
scheduling, we now have a flight simulation running on vxWorks that we
can currently recompile and run on Win98 laptops with *no* code changes
(and no coditionally compied code). Hooray for Ada95!

Of course at 60Hz we get frame overruns all over the place running under
Win98...

--
T.E.D.


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