RE: [uCsimm] Hard Real time Linux

From: Jeff Bauknecht (jbauknecht@premisenet.com)
Date: Thu Feb 24 2000 - 09:06:39 EST


Thanks. We are going to make a custom MB so if we need to add a gate array
we should be able to add it.

Jeff

-----Original Message-----
From: owner-ucsimm@uClinux.com [mailto:owner-ucsimm@uClinux.com]On
Behalf Of Larry Doolittle
Sent: Thursday, February 24, 2000 12:18 AM
To: ucsimm@uClinux.com
Subject: Re: [uCsimm] Hard Real time Linux

Guys -

> > The problem is context switch time. With Hard real time systems
> > it is <10 microseconds. I am trying to find out context switch times in
> > Linux also. There will be several processors and DSP's
> > many pegs many holes
>
> First of all , in my guess, 10 microseconds is really hard!.
> One of the solution for this HARD realtime application could be a
> bufferring scheme. This idea is simple, add another single chip
> (like scenex? 100 mips PIC) doing simple processing
> and do main processing at 1 millsecond interval. But this is
> only useful for periodic request.

On a normal Pentium-class computer, RTLinux folks measure latencies
of about 2 microseconds typical. There is a tail, though. Look
at the Linux Journal article about flying a radar set into a hurricane.

The final extreme is to throw a gate array at the problem. That
can be very inexpensive and general, just imagine Linux running
on the same gate array, see http://www.opencores.org/ OR1K project.
That would give you the flexibility to put the "right" amount of
reflexes in hardware (often that means 10 +/- 0.1 ns delay), and
the remainder in c code, with arbitrary coupling between the two.

    - Larry Doolittle <LRDoolittle@lbl.gov>
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