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

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

  • Re: Polling loop good here???
    ... The "vertical retrace interrupt" was IRQ 2... ... In today's hardware - as has been mentioned - they've almost certainly ... it...make use of the drivers... ...
    (alt.lang.asm)
  • IRQ assignment in Windows 2K/XP/2003...
    ... Both PCI devices request an interrupt and are physically attached to INTA on ... When the drivers load for each of the two devices, ... Sometimes the IRQ ...
    (microsoft.public.development.device.drivers)
  • Re: IRQ assignment in Windows 2K/XP/2003...
    ... >> Both PCI devices request an interrupt and are physically attached to INTA ... >> dynamically assigns an IRQ # for each of the two devices. ... >> the driver during start time? ...
    (microsoft.public.development.device.drivers)
  • Re: IRQ assignment in Windows 2K/XP/2003...
    ... He has two devices behind the bridge, each of which are given separate interrupt vectors by the OS, indicating that the OS believes them to be separately routable. ... Both PCI devices request an interrupt and are physically attached to INTA on ... When the drivers load for each of the two devices, ... Sometimes the IRQ ...
    (microsoft.public.development.device.drivers)
  • Re: [RFC] killing the NR_IRQS arrays.
    ... Subject: IRQ API ... interrupt controllers, and knowing hardware designers, they'll ... I believe that there are some common problems with the existing API ... architecture specific drivers now if they feel they would benefit ...
    (Linux-Kernel)