gerry@dialogic.com (Gerry Lachac) (06/01/91)
I have a question concerning the sharing of interrupts by a device
driver on a PS/2. If I have two drivers that request the same
interrupt using the SetIRQ DevHlp, which ISR (interrupt service
routine) is called first? For example :
Driver A calls SetIRQ(3,ISRa) and later,
Driver B calls SetIRQ(3,ISRb)
When an interrupt 3 comes in, does OS/2 call Driver A's ISR first
(since it was the first set) or Driver B's?
-gerry
--
uunet!dialogic!gerry | "Even a dead plant turns | Dialogic Corporation
OR | over a new leaf | 300 Littleton Rd
gerry@dialogic.UUCP | when the wind blows." | Parsippany, NJ 07054
| | (201)334-8450klos@bcrvmpc3.vnet.ibm.com (Marty Klos) (06/01/91)
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.
gerry@dialogic.com (Gerry Lachac) (06/03/91)
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? -- uunet!dialogic!gerry | "Even a dead plant turns | Dialogic Corporation OR | over a new leaf | 300 Littleton Rd gerry@dialogic.UUCP | when the wind blows." | Parsippany, NJ 07054 | | (201)334-8450
jjr@sgtech.UUCP (John Radigan) (06/04/91)
From article <1991May31.194019.3122@dialogic.com>, by gerry@dialogic.com (Gerry Lachac): > Driver A calls SetIRQ(3,ISRa) and later, > Driver B calls SetIRQ(3,ISRb) > > > When an interrupt 3 comes in, does OS/2 call Driver A's ISR first > (since it was the first set) or Driver B's? I quote from IBM OS/2 Programming Tools and Information 1.2, I/O Subsystems and Device Support, Volume 1, page 2-20. "POSITION RULE An interrupt handler that shares an interrupt level must not depend on its position in the list of handlers for that inter- rupt level." There is no mention of the calling sequence applied by the interrupt manager. -- John Radigan, Star Gate Technologies, Inc., Solon, Ohio Email: jjr@sgtech.uucp Telephone: (216) 349-1860 x666