Tijs van Bakel wrote:
>
> [EMAIL PROTECTED] writes:
>
> > Hi!
> >
> > In RT-Linux Manifesto author writes:
> >
> > "Standard Linux takes up to 600 microseconds to start a handler and can
> > easily be more than 20 milliseconds (20,000 microseconds) late for a
> > periodic task."
> >
> > Is it possible to have 2 miliseconds ? I want to control very fast robot
> > from rt-linux box.
>
> This works for x86 only:
> Try using #define HZ 1024 or some other high number in
> /usr/src/linux/include/asm-i386/param.h
>
> Usually it's 100 and that accounts for the (what I thought were 10) 20
> ms.
>
> Note that this breaks some programs like 'top' and 'ps'
>
> --
> Tijs van Bakel, <[EMAIL PROTECTED]>
Just keep in mind that we're not talking hard real time here! That's the
big difference between standard Linux "real time" and RTLinux real time,
apart from the latency figures. RTLinux can quarantee that Linux and
normal
drivers won't get in the way, so that only the hardware limits the
minimum
latency that can be achieved.
How fast is a very fast robot? :-) Well, I would go for RTLinux control,
especially if it's a powerful machine that might damage both itself and
other
things if it should run out of control.
A missed frame in a game or animated visualization application is no big
deal
(except that I just think it looks cheap and low quality when that
happens),
but failing to decelerate a powerful robot arm in time is a bit worse...
BTW, what kind motor/servo interface? If you try to generate stepper
motor
signals directly from the code, you'll probably need then RTLinux
timing.
While in the case of speed/direction driver cirquitry, it'll probably be
even
more important to make sure the program doesn't stall for a few extra ms
while the motors are running.
Go hard real time and you'll sleep better when the robot is working
night
shifts... ;-)
//David
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