Sharing Interrupts on a PS/2

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2 total messages Started by Marty Klos Fri, 31 May 1991 20:51

#3172

Author: Marty Klos
Date: Fri, 31 May 1991 20:51

23 lines
1399 bytes

References: <1991May31.194019.3122@dialogic.com>

gerry@dialogic.com (Gerry Lachac) writes:
>                    If I have two drivers that request the same
> interrupt using the SetIRQ DevHlp, which ISR (interrupt service
> routine) is called first?

According to the book (see note *):
  "POSITION RULE An interrupt handler that shares an interrupt level
      must not depend on its position int the list of handlers for that
      interrupt level."

My interpretation is that the order is undefined.  Unfortunately,
this does not help you predict how long after an interrupt occurs
before a particular interrupt handler gets control.

* - page 2-20, IBM OS/2 Programming Tools and Information,
    Version 1.2, I/O Subsystems and Device Support,
    Volume 1, Device Drivers

Marty Klos                           | Disclaimer: The statements above
IBM, Boca Raton, FL                  | are my own and not necessarily
Internet: klos@bcrvmpc3.vnet.ibm.com | those of my employer.

Re: Sharing Interrupts on a PS/2

#3173

Author: Gerry Lachac
Date: Mon, 03 Jun 1991 15:08

29 lines
1749 bytes

In article <9105312050.AA16347@ucbvax.Berkeley.EDU> klos@bcrvmpc3.vnet.ibm.com (Marty Klos) writes:
>
>According to the book (see note *):
>  "POSITION RULE An interrupt handler that shares an interrupt level
>      must not depend on its position int the list of handlers for that
>      interrupt level."
>
>My interpretation is that the order is undefined.  Unfortunately,
>this does not help you predict how long after an interrupt occurs
>before a particular interrupt handler gets control.

Agreed.   After looking into this furthur, running some tests, setting
some breakpoints (and looking at the IBM docs - thanks :-), it seems
to me that the interrupt handlers are called at seemingly random
times.  I would venture to guess that maybe the interrupt routines are
called in some round-robin manner for performance reasons.  That seems
reasonable to me.

In level-sensitive mode, the 8259 interrupt controller locks out the
interrupt level if a number of spurious interrupts are received.  Is
it possible to alter this number or disable this feature under OS/2?

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