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SubjectRe: Should I use Linux to develop driver for specialized ISA card?
On Tuesday den 4 September 2001 18:24, Christopher Friesen wrote:
> Fred wrote:
> > I'm curious, Alan, Why? I'm a hardware developer, and I would have
> > assumed that linux would have been ideal for real time / embedded
> > projects? (routers / controllers / etc.) Is there, for instance, a reason
> > to suspect that linux would not be able to respond to interrupts at say
> > 8Khz?
> > of course I know nothing of rtlinux so I'll read.
> I'm involved in a project where we are using linux in an embedded
> application. We've got a gig of ram, no hard drives, no video, and the only
> I/O is serial, ethernet and fiberchannel.
> We have a realtime process that tries to run every 50ms. We're seeing
> actual worst-case scheduling latencies upwards of 300-400ms.
> So while interrupts can be handled pretty quickly, you'll want to make sure
> that your buffers are big enough that your userspace app only needs to run
> every half second or so.
> You may be better off with rtlinux if you need better response. (Or if
> you're on x86 hardware you could look at the low-latency patches.)

1) Why shouldn't the low-latency patches work for another architecture?
Andrew Morton might be interested to fix other architectures too.
(but most patches are not in architecture specific code)

2) Montavistas reschedulable kernel is a very interesting approach, newly
released an update by Robert Love
(there are still some spikes, but the floor is smooth)

But note you with both approaches you want to run the latency critical process
with a higher priority, and probably with the memory locked down.

See example code (latencytest) at:
(but there is no need to run at the maximum possible priority since your
process will be alone anyway...)


Roger Larsson
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