Re: /proc/interrupts - conflicts?

[Brian Mays <brian@debian.org>]

mark@ist.flinders.edu.au (Mark Phillips) writes:

> Can you tell, just by looking at /proc/interrupts, whether there is an
> interrupt conflict?
> 
> In particular, how does it work for pcmcia cards for a laptop?

Well, let's take a look.  Here's what my /proc/interrupts says:

 0:    3736694   timer
 1:      60282   keyboard
 2:          0   cascade
 3:      22149 + serial
 5:          1   sound blaster
 9:     182163   3c589_cs
11:          8   i82365
13:          1   math error
14:     351147 + ide0

Here's what this means:

Interrupt  0: the timer
Interrupt  1: the keyboard
Interrupt  2: same as 9
Interrupt  3: my serial mouse
Interrupt  5: my sound card
Interrupt  9: my PCMCIA network card
Interrupt 11: the PCMCIA controller
Interrupt 14: my hard drive

You can search for conflicts caused by the PCMCIA utilities by listing
the contents of /proc/interrupts with the PCMCIA card manager disabled
(execute as root `/etc/init.d/pcmcia stop') and observing at what
interrupts are being used.  On my system, the sound card likes to use
irq 5.  Therefore, I exclude this interrupt from being used by a PCMCIA
card by placing the following line in /etc/pcmcia/config.opts:

exclude irq 5

Without this line, my sound card does not work sometimes because the
PCMCIA system seizes irq 5.  This is evident in /proc/interrupts as a
line such as

 5:       2149   3c589_cs

This shows that irq 5 has been assigned to my PCMCIA network card and
hence is not available for use by the sound card.

When worrying about interrupt conflicts, keep in mind that use irq 4
is often used for the first and third serial ports and irq 3 is often
used for the second and fourth serial ports.  The parallel port likes
to use irq 7, so you might want to exclude it in config.opts if you
are hooked up to a printer or are using plip to connect to another
computer.  If, however, you never use your parallel port and your
PCMCIA cards at the same time, then you probably don't need to worry
about it.

Brian


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