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Re: Maximum RTC Tick Rate


On Wed, 2003-02-12 at 16:55, Fred Woolsey wrote:
> Does anyone have info on the maximum real-time clock tick frequency that
> eCos can handle on an i386 platform?  I've built a test app with a tick
> interval of 100 us, which appears to work OK.

One way to determine this would be to run the standard
test 'tm_basic' with CLOCK_LATENCY turned on.  This will
tell you not only the time to service the clock interrupt,
but also the DSR and ISR latencies associated with it.

My guess is (depending on your actual hardware) that at
a clock rate of 100us/tick, you're probably spending a
fairly considerable percentage of time just processing
those interrupts (e.g. if the "round trip" time for the
clock tick as measured by 'tm_basic' is 10us, then you
would be using 10% of the CPU just to handle the clock
at that rate).

The maximum clock rate would thus be related to how fast
your hardware is and how much of the CPU you are willing
to give up just to process the clock.

-- 
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|       Mind: Embedded Linux and eCos Development        |
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| Gary Thomas              email:  gary.thomas@mind.be   |
| Mind ( http://mind.be )  tel:    +1 (970) 229-1963     |
| gpg: http://www.chez-thomas.org/gary/gpg_key.asc       |
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