Re: [PATCH] local_irq_disable removal

[Paulo Marques <pmarques@grupopie.com>]

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)