PNP(3)PNP(3)NAME
pnp, pci - Plug 'n' Play ISA and PCI Interfaces
SYNOPSIS
bind -a '#$' /dev
/dev/pci/bus.dev.fnctl
/dev/pci/bus.dev.fnraw
/dev/pnp/ctl
/dev/pnp/csnnctl
/dev/pnp/csnnraw
...
DESCRIPTION
This device provides a limited interface to the PCI bus and Plug 'n'
Play ISA devices. Both are present on most PC platforms; on others,
only the pci interface is present (because there is no ISA bus).
PCI Interface
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 read to obtain the raw contents 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‐
ber.
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
plan9.ini:
pnp0=port=0x203
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
following command:
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‐
mented yet.
A mechanism is provided for configuring cards via plan9.ini(10.6). 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
intention 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‐
mented.
EXAMPLES
To list all PCI functions:
cat /dev/pci/*ctl
To find just the PCI video card (class 3):
grep '^03' /dev/pci/*ctl
SOURCE
/os/pc/devpnp.c
/os/port/devpci.c
BUGS
There is currently no way to write to PCI configuration space, or to
perform reads of less than 32 bits. 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
been implemented.
There should be a user program for identifying and configuring Plug 'n'
Play cards.
PNP(3)
