Re: [CAD_CAM_EDM_DRO] Re: Multitasking

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On 2000-10-16 Ken Jenkins wrote:

> I don't know exactly what "realtime" means in that nothing
> happens "instantaneously"<snip>

Well, there are two kinds of "Realtime" - "Soft" and "Hard". In
"Soft" realtime, and event (whatever the event IS), will NEVER miss
an
event, and will process the event BEFORE the next event comes along,
but does not have fully assured latency. "hard" realtime has an
assured latency. You are guaranteed that the processing of an event
will take no more than X time, and any events that take place during
that time are queued, OR that some events will interrupt other
events,
because they have priority.

In reality, MOST milling, except, as far as I can see, thread
milling,
requires only "soft" realtime. If the mill moves at 99 IPM instead
of
100 ipm, it's not the end of the world. Threading on a lathe
requires
hard real time, unless the controller actually steps the spindle (NOT
just reading spindle position from an encoder)

Back when, I used to do "soft" realtime programming. It didn't
matter
how long it took me to come back (within reason <g>), but I had to
process ALL events. A latency on that system could run from 1 ms out
to as much as 2 minutes, but everything got processed in order, and
all events were handled (eventually)

Charlie

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