Re: how high the output frequency can achieve in RTLinux

Since there are counter/timer boards which can be programmed to output
periodic signals above a Megahertz, I assume that what you really mean is
how high rate a periodic task you can reach with RTLinux.  The same is true
of analog output boards with programmable DMA.

Since an ISA bus runs at 8 MHz and requires several clock cycles to even
write a single value to a port, you'd be limited to no more than 1-2 MHz
with any ISA bus device.  Since the bus is the rate limiting factor here,
even a modest few hundred Megahertz CPU could potentially do this, BUT the
question is, how can you regulate the speed?  One answer with a
Pentium-class CPU is to use the CPU's clock-rate counter register and take
over the CPU completely, using a busy-wait loop to do the pacing.  If you
have a PCI-bus device instead of an ISA-bus device, you could probably get
an output signal to maybe 2-8 MHz to the exclusion of everything else.

Once you decide to use interrupts to pace the process, you're limited by the
speed of RTLinux's interrupt latency which, even for PCI interrupt sources,
is on the order of a few microseconds so you couldn't get much beyond a very
small number of hundreds of kilohertz, maybe 300 KHz at the outside.

As a practical matter, I have in the distant past used a 66 MHz '486 to run
a periodic task at ~20-40 KHz for long periods of time.

Perhaps if you were more precise in explaining what you wanted to do, we
could be of more help.

    Norm

----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>
Sent: Sunday, January 23, 2005 9:11 AM
Subject: [Rtl] how high the output frequency can achieve in RTLinux


>
> Hello,everybody!
> Now I'm trying using RTLinux to output some sigals.I wonder how high the
output frequency can achieve if I use RTLinux(All other factors are
ignored)!Maybe you have some idea.Any suggestion will be appreciated!Thanks!
> Erik
> China University of Mining and Technology,Beijing
>
> _______________________________________________
> Rtl mailing list
> [email protected]
> http://www2.fsmlabs.com/mailman/listinfo/rtl

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