Wireless issues...

John dingo at coco2.arach.net.au
Sun Sep 19 12:13:59 UTC 2004

Matthew Garrett wrote:

>It seems to be a problem with newer kernels. The parallel port drivers
>seem to grab IRQ 7 and refuse to let anything else use it. If the
>parallel port driver is loaded after everything else, it will realise
>that it can't have the interrupt and use polling instead.
The parallel port is an ISA port, and IRQ is dedicated to that port: ISA 
interrupt lines are edge-sensitive (they trip on change of voltage) and 
so are not sharable.

In most BIOSes _can_ configure that IRQ as reserved, or you can 
configure the printer port to another standard location (and maybe only 
move the problem).

Once the printer driver is loaded and grabbed its IRQ, nothing else 
should touch it.

Pretty much all the IRQs below 8 have standard assignments; 2==9 because 
it's used to cascade a second programmable interrupt controller (PIC).

I don't recall now what all the standard assignments are, but devices 
using them include
Two serial ports
Two printer ports

That doesn't leave many out of the eight in the original PC.
IRQ 12 is hardwired to the PS/2 mouse. Available if you don't use one.
IRQ 14 used by IDE0.
IRQ 15 was reserved then used by IDE1.

Soundblaster cards, NICs, SCSI cards & such typically pinched a printer 
IRQ, or maybe a serial port IRQ, and that lead to configuration 

Modern PCs don't have ISA slots, but they stll have a few ISA devices on 
the motherboard.

However, it seems the end of the problem is nigh: here are the interrupt 
assignments from my Athlon:
summer at Glider:~$ cat /proc/interrupts
  0:   35483261    IO-APIC-edge  timer
  1:         10    IO-APIC-edge  i8042
  7:          2    IO-APIC-edge  parport0
  8:          4    IO-APIC-edge  rtc
  9:          0   IO-APIC-level  acpi
 14:      93651    IO-APIC-edge  ide0
169:     843583   IO-APIC-level  ide2, ide3
177:          0   IO-APIC-level  SiS 7012
185:         45   IO-APIC-level  ohci_hcd
193:        183   IO-APIC-level  ohci_hcd
201:     833638   IO-APIC-level  ehci_hcd
209:    9668866   IO-APIC-level  eth0
NMI:          0
LOC:   35484318
ERR:          0
MIS:          0
summer at Glider:~$

"level" is good. The signal remains active while any device asserts it, 
so all the devices using it can be handled.

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