Re: Sharing real time interrupts with linux kernel interrupts

On Fri, 3 Sep 2004, Der Herr Hofrat wrote:

>> Hello to all!
>>
>>
>> I would like to share the Linux kernel space interrupts with a rt task.
>>
>>
>> When an interrupt arrives, the rt task check if the interrupt is from
>> the specific hardware of the task. If not, the rt task redirect the
>> interrupt to Linux kernel (like a software interrupt).
>>
>> How I implement this? Someone have some ideas?
>>
> Basically all you would need to do in the RT-isr is
> to check if the irq is from the RT-device and if not
> then mark the interrupt pending, when the rt-system is
> idle then the next non-rt interrupt (that is atleast the
> next timer interrupt) would hand the interrupt on to Linux
>
> give main/rtl_core.c:rtl_intercept  a look.


Yeah, exactly what Hofrat said.


Here's a pseudocode example of this (actually this is code taken from my 
driver):

static unsigned int interrupt_handler_rt(unsigned int irq,
 					 struct pt_regs *regs)

{
   (void)regs;

   board_handle_interrupt(); /* This sets interrupt_was_for_me */

   if (interrupt_was_for_me) {  /* Force this IRQ enabled right now if
                                   this interrupt was for me, so as to
                                   immediately invoke this handler again
                                   if another interrupt is waiting.. */

     /* rtl_hard_enable_irq tells the IRQ controller to turn on a
        particular IRQ right *now*.

        This hangs the system if called unconditionally -- DESPITE what the
        RTLinux docs will tell you!   */

     rtl_hard_enable_irq(irq);

   } else {

   /* Now, pend the IRQ to linux if the interrupt wasn't for me.

      NB: I am not sure if this can mean interrupts could potentially be
      lost if the board and a different board both asserted the same IRQ
      line at the same time.  I am assuming that can't happen, so I only pend
      the IRQ to linux if the interrupt wasn't for me. */

     rtl_global_pend_irq(irq);
   }

   return 0;
}

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