While looking into how to implement sharing of interrupts between realtime and non-realtime domains (and applying Wolfgang Grandegger's patch [https://mail.gna.org/public/xenomai-core/2006-01/msg00233.html], which is necessary to make XN_ISR_ENABLE work at all on the PowerPC platform), I'm beginning to think that XN_ISR_CHAINED and XN_ISR_ENABLE are mutually exclusive, since if both are set, desc->handler->end will be called twice:

  1. When the realtime isr handler returns
  2. When the Linux domain calls it in __do_IRQ

In the solution I have in mind at the moment, I will:

  1. Add an extra iend handler argument to xnintr_init
  2. If XN_ISR_ENABLE is returned from the isr handler,
     replace desc->handler->end with the user supplied
     iend handler.

Hereby I hope to be able to handle interrupts shared between realtime and non-realtime domain, without having the realtime domain wait for all non-realtime interrupts to finish. This is the scenario I'm thinking of:

  1. A non-RT interrupt occurs
  2. The (RT) isr handler detects the non-RT interrupt,
     disables further non-RT interrupts on that irq-vector, replaces
     desc->handler->end with the user supplied iend handler,
  3. RT interrupts are serviced by the (RT) isr handler,
     returns XN_ISR_ENABLE
  4. The Linux domain get a chance to run the chained interrupt,
     and eventually calls desc->handler->end (supplied iend handler)
  5. The iend handler reenables non-RT interrupts.

Comments on the above are most welcome!


Anders Blomdell

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