1. PCI configuration in Linux 2.2.18 : IRQ assignment?
I have an old Pentium 90 PC with one PCI slot free, and I am trying to
replace the old 28.8 Kbps ISA modem with a modern 56 Kbps PCI modem. The
new modem will *have* to work in both Linux 2.2.18 and Windows 95.
I have read the Plug-and-Play HOWTO. I also appreciate that I *could*
use a 56 Kbps external modem at a pinch, except that I have enough plugs
and adapters on my single power-point as it is. One more would cross the
line from crazy to dangerous.
The ISA modem is on IRQ 4, which I freed up from one of the
motherboard's serial ports. The other serial port was on IRQ 3, which I
have also freed. IRQs 5 and 9 belong to an ISA-PnP soundcard, 7 belongs
to the motherboard's parallel port, 10 is used by a PCI card providing 2
USB ports, and 11 is used by a PCI video card. (Typically, anyway!) I
boot as a PnP OS for the sake of Windows 95.
Basically, I will have IRQs 3 and 4 available for the new modem.
However, I'm concerned that any new PCI card will not get configured to
use either, because I tested adding another PCI card and it was
configured to use IRQ 9 instead! This caused a conflict with the
soundcard of course.
I have also experimented with setpci to change the INTERRUPT_LINE value
for the PCI USB-port card (from 10 to 3), and discovered that it didn't
make the slightest bit of difference which IRQ I wrote into the bus. Is
this information written by the BIOS purely for reference? The output
from lspci did not change, and /proc/interrupts showed that the USB uhci
module always used IRQ 10 anyway. Is there any way that I could actively
reassign the IRQs to ensure that Linux gets it right? I am assuming that
Windows is PnP-enough to sort itself out! (yeah, right ...)
To my knowledge, the BIOS has never assigned any device to use IRQ 3,
despite this IRQ currently being free. As I mentioned earlier, the USB
hub uses 10, the video card uses 11 and any new PCI card was given IRQ 9
where it conflicted with the ISA-PnP soundcard. Is there something
special about IRQ 3? I *did* check with the BIOS, and it regards both
IRQs 3 and 4 as available for PnP.
The soundcard is an Ensoniq SoundScape, and uses the sscape module with
sscape irq=5 dma=1 io=0x338 mpu_io=0x330 mpu_irq=9
This module refuses to load without the mpu_io and mpu_irq options.
However, IRQ 9 never appears in /proc/interrupts even when it is loaded.
Could the BIOS somehow be unaware that the soundcard needs it? If so,
why? Marking an IRQ as "reserved for a legacy ISA card" is not an option
when booting as a PnP OS, BTW.
Thanks for any help with any of this. And the sooner the ISA bus bites
the dust, the better :-)!!!
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