DPRG mailing list archives: [DPRG] Processing unit for mobile robot

Wed Apr 23 13:09:28 CDT 2008

ed at okerson.com said: Wednesday, April 23, 2008 8:23 AM
> Today I would probably go with one of the many smaller 
> processors capable of running Linux, but it could still be 
> done witn a PC.  My current favorite is the AVR32 processor 
> from Atmel.  ... Real time processing on 
> Linux is now easier than ever.

Hi Ed, there was a big discussion on the PARTS list where Robert
F. Scheer was prep'ing his Outdoor Challenge Robot, and intended
to use Linux in a real time mode, and found he couldn't get more
than (something like) 20 updates a second from his remote micro
without horrible jitter in the time of the messages arrivale,
even though he had been sold on the idea of Linux as very real
time capable, so he abandoned the idea of doing PID on the PC
and moved it out to the external AVRs (appologies if I got
details slightly off, if someone was following that more closely
than I, feel free to make a more accurate report).

Now my basic opinion is today with a program like LabVIEW I can
get to 1mS timings on the PC even under windows, but Robert had
problems, and many suggestions on Linux settings were discussed.
I didn't follow that part because I have never used Linux, nor
do I understand the desire to do so.

So! Maybe you want to expound on Linux a bit, and tell us 1)
what is the real nature of the realtime limits of Linux and 2)
Why Linux anyway? 

For me Linux is just so much interference in my way, preventing
me from getting the real time stuff I've been able to do for
years without an operating system in the way nearly impossible
to get right and under the same control I have with a micro
without an OS in the way. I recognize I could run some PC
applications so maybe I could do some vision processing, and
some networking that would be beyond my experience of doing with
a micro, but to me, this stuff isn't robotics. It isn't the
stuff that makes the robot move. So I just don't get the
excitement about getting Linux on to a processor so it can be in
my way. What do you suppose I'm missing that you see as so
desireable?

Randy