Gene Heskett wrote:
[...]
Lets add the operation of 4 or more stepper motors in real time for
smaller milling machines. There, the constraints are more related to
maintaining a steady flow of step/direction data at high enough
speeds to make a stepper, with 8 microsteps per step, and 240 steps
per revolution, run smoothly at speeds up to say 20 kilohertz, or 50
microseconds per step, maintaining that 50 microseconds plus or minus
not more than 5 microseconds else the motors will start sounding
ragged and stuttering.
This is the kind of problem that is screaming "give me dedicated
hardware!". Why would one spend $500+ on a PC to do the work of a $2
microcontroller (and possibly throw in an FPGA to the mix)?. Not to
mention that the microcontroller/FPGA would maintain 50us +/- 0us
instead of the 50 +/- 5 you've mentioned.
The same goes for the "hand under the saw". A simple
transistor/triac/whatever and a logic circuit would stop the saw, we
don't need any real time OS for that (and I would certainly trust the
logic circuit more than any real time OS :).
IMHO, the kind of problems where real time OS's are useful are the kind
that require computational power while having real-time constraints.
Like the sound effects processor for the guitar that Lee Revell already
mentioned or controlling an airplane in flight that has to measure a lot
of sensors, do some state space calculations with some not-so-small
matrices (together with Kalman filtering, etc.) and move the actuators.
--
Paulo Marques - www.grupopie.com
An expert is a person who has made all the mistakes that can be
made in a very narrow field.
Niels Bohr (1885 - 1962)
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