Re: IRQ assignment in Windows 2K/XP/2003...

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

Why do you say that the motherboard has them or'd together? The Int A lines
do not need to be bussed together. The mother board can route the Int lines
from each slot anyway it wishes.

Paul
"Mark Roddy" <markr@xxxxxxxxxxxxxx> wrote in message
news:%23y$Xs5kOFHA.2356@xxxxxxxxxxxxxxxxxxxxxxx
> Cosmo wrote:
>> OS: Windows 2K/XP/2003
>> Hardware Platform: Intel x86-based PC, PIII, 815E chipset
>> Drivers: WDM-style
>>
>> I have two independent, single-function PCI devices on the other side of
>> a
>> PCI-to-PCI bridge:
>>
>> PCI slot <---> PCI-to-PCI bridge <---> PCI device #1
>> |
>> ---> PCI device
>> #2
>>
>> Both PCI devices request an interrupt and are physically attached to INTA
>> on
>> the PCI bus. A seperate WDM device driver is written to control each of
>> the
>> PCI devices.
>>
>> When the drivers load for each of the two devices, the system (PnP
>> manager)
>> dynamically assigns an IRQ # for each of the two devices. Sometimes the
>> IRQ
>> # is the same and sometimes the IRQ # is different. I can disable and
>> re-enable each device via the Windows XP Device Manager and get the IRQ #
>> assignments to change.
>>
>> Now, when the two devices are assigned a common IRQ # and INTA is
>> asserted
>> by either device, the ISR in each of the drivers is called to determine
>> if
>> they are interrupting (one says no and the other says yes--hardware is
>> serviced and all is well). However, when the two devices are assigned
>> different IRQ #s, only the ISR for one of the drivers is called. If the
>> other device happened to be generating the interrupt, the system is
>> locked
>> up as the non-interrupting device's ISR is continually called in a loop.
>>
>> I am inclined to believe that as long as the two PCI devices are assigned
>> different IRQ #s by PnP when they both use the same INTA interrupt line
>> on
>> the PCI bus, both device's ISRs are not guaranteed to be consulted.
>>
>> What can be done to cure this problem? Can something different be done
>> in
>> the driver during start time? In the IoConnectInterrupt() call? Right
>> now
>> I am simply passing the information handed to the driver by the PnP
>> manager
>> into the IoConnectInterrupt() call. Any other options? Can anything be
>> done to the PCI configuration space of the end-devices or PCI-to-PCI
>> bridge
>> to influence the system's choice of IRQ #? I would like to understand
>> this
>> behavior better (what is going on under the covers).
>>
>> Regards,
>> Cosmo
>>
>>
> My PCI book says that the interrupt lines on your pci devices are directly
> connected to the same interrupt lines on the connector slot your bridge is
> plugged into. In other words, for interrupts, the bridge is not really in
> the picture. So the situation appears to be that the OS thinks that these
> devices have separately routable interrupts when in fact they motherboard
> has them or'd together. So somebody is confused. The choices are: me, the
> bios, or the os.
>
>
> --
>
> =====================
> Mark Roddy DDK MVP
> Windows 2003/XP/2000 Consulting
> Hollis Technology Solutions 603-321-1032
> www.hollistech.com


.

Relevant Pages

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