BeOS Driver Tips and Tricks

Subject: Re: dev #3033: aliens generating interrupts?
  Date: Wed, 2 Apr 1997 17:02:59 -0800
  From: William Adams 
    To: thorns@cs.mcgill.ca

>Subject: Re: dev #3033: aliens generating interrupts?
>To: William Adams 
>Date: Wed, 2 Apr 1997 12:29:34 -0800 (PST)
>
>This message is generated when the processor get interrupted, but when
>it goes to look at the interrupt source register, none of the
>interrupt sources appear to be interrupting.
>
>This typically happens because of a device driver bug.  Once common problem
>is that the device driver's interrupt handler is calling
>release_sem instead of release_sem_etc with the DO_NOT_RESCHEDULE
>flag set, and then doing something to clear the interrupt on the
>actual device hardware.  Since calling release_sem does in fact cause
>a reschedule, the interrupt handler will continue running 'later', possibly
>even on another processor (on beboxes and MP macs).  If the device in the
>meantime has another interrupt ready, and the interrupt handler then clears
>the interrupt, you lose an interrupt!
>
>If the clearing happens at just the right time, i.e after the device has
>generated the interrupt causing the cpu taking i.o interrupts to be
>interrupted, but before that cpu can read the interrupt source register,
>you get the wonderful 'ALIENS...' message.
>
>>
>>Anyone want to comment on this.
>>-- William
>>
>>>Date: Tue, 1 Apr 1997 20:53:32 -0500 (EST)
>>>To: devsupport@be.com
>>>Subject: dev #3033: aliens generating interrupts?
>>>From: Simon Thornington 
>>>
>>>I just got a message on serial4 as follows:
>>>
>>>ALIENS ARE GENERATING INTERRUPTS! CALL BOB 80005ec4 40220020
>>>
>>>I wouldn't think anything of it, except that I am writing a device
>>>driver and have been having problems with interrupts that don't appear
>>>to be from me.  What does this message mean?
>>>
>>>Cheers,
>>>
>>>Simon.
>>>