Re: how high the output frequency can achieve in RTLinux

On Sunday 23 January 2005 16:16, Norm wrote:
> 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
> >
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