New HOWTO: Plug-and-Play-HOWTO - page 8
Table of Contents
7. What Is My Current Configuration?
Here "configuration" means the assignment of PnP bus-resources
(addresses, IRQs, and DMAs). There are two parts to this question for
each device. Each part should have the same answer.
1. What is the configuration of the device driver software? I.e.:
What does the driver think the hardware configuration is?
2. What configuration (if any) is set in the device hardware?
Of course the configuration of the device hardware and its driver
should be the same (and it normally is). But if things are not
working right, it could be because there's a difference. This means
the the driver has incorrect information about the actual
configuration of the hardware. This spells trouble. If the software
you use doesn't adequately tell you what's wrong (or automatically
configure it correctly) then you need to investigate how your hardware
devices and their drivers are configured. While Linux device drivers
should "tell all" in some cases it's not easy to determine what has
been set in the hardware.
Another problem is that when you view configuration messages on the
screen, it's sometimes not clear whether the reported configuration is
that of the device driver, the device hardware, or both. If the
device driver is assigned a configuration and then checks the hardware
out to see if it's configured the same, then the configuration
reported by the driver should be that of both the hardware and the
But some drivers which don't do this may accept a configuration that
doesn't check out. For example, "setserial" will accept a
configuration that doesn't check out and thus may only be telling you
the configuration of the driver and not the hardware.
7.1. Boot-time Messages
Some info on configuration may be obtained by reading the messages
from the BIOS and Linux that appear on the screen when you first start
the computer. These messages often flash by too fast to read but once
they stop type Shift-PageUp a few times to scroll back to them. To
scroll forward thru them type Shift-PageDown. Typing "dmesg" at any
time to the shell prompt will show only the Linux kernel messages and
miss some of the most important ones (including ones from the BIOS).
The messages from Linux may sometimes only show what the device driver
thinks the configuration is, perhaps as told it via an incorrect
The BIOS messages will show the actual hardware configuration at that
time, but isapnp, or pci utilities, or device drivers may change it
later. The BIOS messages are displayed first before the ones from
Linux. As an alternative to eventually using Shift-PageUp to read
them, try freezing them by hitting the "Pause" key. Press any key to
resume. But once the messages from Linux start to appear, it's too
late to use "Pause" since it will not freeze the messages from Linux.
7.2. How Are My Device Drivers Configured?
There may be a programs you can run from the command line (such as
"setserial" for serial ports) to determine this. The /proc directory
tree is useful. It seems that there are many files buried deep in
this tree that contain bus-resource info. Only a couple of them will
be mentioned here. /proc/ioports shows the I/O addresses that the
drivers use (or try if it's wrong). They might not be set this way in
/proc/interrupts shows only interrupts currently in use. Many
interrupts that have been allocated to drivers don't show at all since
they're not currently being used. For example, even though your
floppy drive has a floppy disk in it and is ready to use, the
interrupt for it will not show unless its in use. Again, just because
an interrupt shows up here doesn't mean that it exists in the
hardware. A clue that it doesn't exist in hardware will be if it
shows that 0 interrupts have been issued by this interrupt. Even if
it shows some interrupts have been issued there is no guarantee that
they came from the device shown. It could be that some other device
which is not currently in use has issued them. A device not in use
(per the kernel) may still issue some interrupts for various reasons.
7.3. How Are My Hardware Devices Configured?
It's easy to find out what bus-resources have been assigned to devices
on the PCI bus with the "lspci" or "scanpci" commands. For for
kernels < 2.2: see /proc/pci or /proc/bus/pci for later kernels. Note
that IRQs for /proc/pci are in hexadecimal. Don't bother trying to
decipher /proc/bus/pci/devices since "lspci" will do that for you.
For the ISA bus you may try running pnpdump --dumpregs but it's not a
sure thing. The results may be seem cryptic but they can be
deciphered. Don't confuse the read-port address which pnpdump "tries"
(and finds something there) with the I/O address of the found device.
They are not the same. To try to find missing hardware on the ISA bus
(both PnP and legacy) try the program "scanport" but be warned that it
might hang your PC. It will not show the IRQ nor will it positively
identify the hardware.
Messages from the BIOS at boot-time tell you how the hardware
configuration was then. If only the BIOS does the configuring, then
it should still be the same. Messages from Linux may be from drivers
that used kernel PnP functions to inspect and/or set bus-resources.
These should be correct, but beware of messages that only show what is
in some configuration file (what the driver thinks). Of course, if
the device works fine, then it's likely configured the same as the
Some people use Windows to see how bus-resources have be set up.
Unfortunately, since the hardware forgets its bus-resource
configuration when powered down, the configuration may not be the same
under Linux. It sometimes turns out the same, but Windows and Linux
do not necessarily use the same logic in configuring. Many devices
have bus-resource preferences that are often adhered to by both Linux
and Windows. But don't count on devices being configured the same.