Interrupt Design Q

Jared Silva jsilva at
Fri Oct 8 13:51:28 CEST 2004

I have a function that is called whenever the parallel port receives an
interrupt.  The interrupt is received from an external function
generator, which sends square waves at a frequency that I choose.

Now, if the frequency is set low and the function is called by the
interrupt, there will not be any issues.

However, what if the frequency is set higher, so that when the next
interrupt is received, the function is still running from the previous
interrupt?  In other words, the previous calculation or whatever is
still not finished, even though it should be.

How can I flag this?  Can I simply set a static or global variable as a
flag within the function?  On the other hand, do I need to do something
RTAI specific?

As of now, I use the following calls to set up the IRQ handler:
- rt_request_global_irq
- rt_startup_irq
- rt_shutdown_irq
- rt_free_global_irq


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