PNP(3)PNP(3)NAMEpnp - Plug 'n' Play ISA and PCI Interfaces
bind -a '#$' /dev
This device provides a limited interface to the PCI bus and Plug 'n'
Play ISA devices.
PCI devices are addressed logically by a bus number, a device number on
that bus, and a function number within the device. The set of all such
device functions may be enumerated by traversing the /dev/pci direc‐
tory; the driver serves two files for each function. These are a con‐
trol file which may be read for a textual summary of the device func‐
tion, and a `raw' file which may be used to read or write the raw con‐
tents of PCI configuration space.
The first field of a PCI control file contains the class, sub-class and
programming interface values for the device function, expressed as
2-digit hexadecimal values, and separated by periods. The second field
yields the vendor ID and device ID, each as 4-digit hex numbers, sepa‐
rated by a slash. The third field is the associated interrupt line in
decimal. The remainder of the line enumerates any valid base address
registers for the function, using two fields for each. In the first
field, the index of the register is followed by a colon, and then the
value of the register itself. The following field gives the associated
size of the memory (or I/O space) that is mapped by the register.
Plug 'n' Play
Plug 'n' Play ISA devices are discovered by sending a fixed `unlock'
sequence over an I/O port, and then reading back data from another
port. An arbitration algorithm is used to separate out the individual
cards and enumerate them in turn. Each card is assigned a unique num‐
ber, called a CSN, in the range 1-255 as a result of enumeration.
Cards also have a fixed 64 bit identification number, set by the manu‐
facturer, which is used by the arbitration algorithm to resolve con‐
flicts. The first 32 bits describe the type of the card, and the sec‐
ond 32 bits form a serial number for the particular instance of that
card type. When formatted textually, it appears as 3 upper-case let‐
ters (typically representing the manufacturer), followed by 4 hex dig‐
its, then a period, then 8 hex digits. The substring before the period
is the card type, and the substring after the period is the serial num‐
The enumeration algorithm needs to be enabled by specifying the port
number to write the unlock sequence out on. This can be configured to
take place at boot time by adding a line like the following to
Here port should be chosen to not conflict with any existing devices.
It must be in the range 0x203-0x3ff. Alternatively, one can use the
echo port 0x203 >/dev/pnp/ctl
Note that a side-effect of PnP enumeration is to reset the configura‐
tion state of all such cards; any settings made by a Plug and Play BIOS
will be lost. Reading the file /dev/pnp/ctl returns one of the strings
enabled port or disabled.
For each enumerated card, two files are served in /dev/pnp. A control
file may be read to determine the ID of the card, and a raw file may be
read to obtain the configuration data associated with the card. It is
intended that the control file should take commands which set the vari‐
ous configurable resources of the card, but this has not been imple‐
A mechanism is provided for configuring cards via plan9.ini(8). A line
of the form pnpn=idstring ... will cause the driver to look for the
card named by idstring and, if found, assign it the CSN n. The inten‐
tion is that any additional text after the idstring is interpreted as
if it was written to the card's ctl file, but this is not yet imple‐
To list all PCI functions:
To find just the PCI video card (class 3):
grep '^03' /dev/pci/*ctl
Access to the I/O and memory regions of a PCI device is not provided.
The ability to set a Plug 'n' Play card's configurable settings has not
There should be a user program for identifying and configuring Plug 'n'