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SubjectRe: Definition of "realtime"
On Fri, 2 Oct 1998, Olaf Titz wrote:

> An example cited here is the Windoze printer which needs all of the
> data for one line of pixels coming in in exactly the speed with which
> the drum moves (or at least I think this is the way those devices
> work). When the CPU delivers the data late, the page has moved
> away and the result, i.e. printed page, is _not correct_, regardless
> of whether it comes out distorted, blank or the printer jams and needs
> the big switch.

hmm, ...

I've learned you need realtime capable systems only, if the problem you
have to solve can't be solved otherwise. Should read, if the process your
are controling is not predictable, such that you can't 'buffer' counter
mesures. In the above 'printer' case, you _can_ buffer and simply avoid
that problem by designing the hardware more flexible.

Given your software is controling the flight of an airplane, you can't
predict what steering information you will get next from the radar,
hence you have to react in the given time slot and 'buffering' is not
impossible.

If you define 'realtime' the way you did, even doing a refresh for a
dynamic RAM chip is a realtime condition, but you know, this problem
was solved otherwise ;-)

Hans
<lermen@fgan.de>


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