[ECOS] Interrupt latency

David Vrabel dvrabel@arcom.com
Thu Nov 20 13:02:00 GMT 2003


>     i am using i386 PC based platform. and UART is 16c550 with FIFO is
> disabled.i am not able to find out the interrupt latency for each
> charecter that i received. could u please send me the rough figures if
> any body calculated or having rough idea of how much it will be.

You'll need to measure it yourself as it's very system dependant.  I've 
used a 'scope for this in the past.

For example, with a 25MHz i386EX doing nothing extra but timer 
interrupts and a trivial external interrupt whose handler does nothing 
but toggle a GPIO line I got the following results:

                  Typical  Maximum[*]
ISR latency/us        22       74
DSR latency/us       108       90

Throw in some ethernet traffic...

                  Typical  Maximum[*]
ISR latency/us        24       92
DSR latency/us       110      544

David Vrabel

[*] Maximum in about 1.2 million samples.
David Vrabel, Design Engineer

Arcom, Clifton Road           Tel: +44 (0)1223 411200 ext. 3233
Cambridge CB1 7EA, UK         Web: http://www.arcom.com/

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