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wl (4)
>> wl (4) ( FreeBSD man: Специальные файлы /dev/* )
BSD mandoc
NAME
wl
- T1 speed ISA/radio lan card
SYNOPSIS
device wl0 at isa? port 0x300 irq 5
DESCRIPTION
The
driver controls a radio lan card system made originally by
NCR, then ATT, now Lucent.
The system is spread-spectrum radio
at around 915 MHz (or 2.4 GHz).
With the supplied omni-directional antennae,
about 400 feet (indoors, more outdoors) can be covered in circumference.
This card can talk to the companion (wlp0) pccard.
Speeds vary
from 1 megabit to theoretically 2 megabits (roughly T1 in speed).
The card has three fundamental hardware
units, a so-called PSA or programmable storage area, a radio modem,
and a Ethernet lan controller.
The latter component is the
ancient (and not very honorable) Intel 82586 Ethernet chip.
Fundamentally it appears to the operating system as an Ethernet system,
and speaks IEEE MAC addresses.
The radio modem simply translates
Ethernet packets to/from radio packets, that are either at 2.4 GHz
or 915 MHz depending on the radio modem.
It supports a collision
avoidance scheme.
The lan controller
supports promiscuous mode, broadcast, and multicasting
(although there is a glitch
in the latter).
"It thinks it is Ethernet".
How it is used
depends on the kind of antennae deployed with it.
Point to point
applications are possible as are Ethernet-like lan use.
The vendor
ships an omni-directional antennae that works in the
vicinity of 400 feet (indoors).
Point to point antennae can be purchased that will go miles.
SETUP
The card can either be initialized with the vendor supplied DOS setup software.
Typically minimally an IRQ, port, and Network ID must be supplied.
Michael Smith's
wlconfig(8)
utility can now be used to do this work from
the UNIX side.
The card is "not" plug and play.
The network id controls whether one set of cards can hear another.
If different, cards will read physical packets, but they will be discarded
by the radio modem.
CONTROL
In addition to the config utility, there are several sysctl
switches that can be used to modify runtime parameters.
The
sysctl(8)
variables are as follows:
"machdep.wl_xmit_delay <useconds>"
This variable will cause the driver to insert a delay on transmit.
250 is the default.
The delay should probably be a bit longer
on faster cpus and less on slower cpus.
It exists because the 82586
was not designed to work with Pentium-speed cpu systems and if overdriven
will have copious xmit side errors.
machdep.wl_ignore_nwid <0 | 1>
This switch defaults to 0; i.e., the nwid is not ignored.
It can
be set to 1 to cause the nwid to not be used.
This may be useful
when the device is in promiscuous mode as one can watch for all
packets and ignore nwid differences.
machdep.wl_xmit_watch <milliseconds>
This switch is not currently useful.
machdep.wl_gather_snr <milliseconds>
This switch is not currently useful.
There is also a signal strength cache in the driver.
It may be interrogated
with
wlconfig(8).
Incoming packets
are checked for certain hardware radio-modem values including signal
strength, silence, and quality, which range fro 0..63, 0..63, and 0..15
respectively.
Thus one can read out signal strenth values to see
how close/far peer nodes are.
The signal strength cache is indexed by
sender MAC address.
There are two sysctls that change how it filters packets.
Both are on
by default.
machdep.wl_wlcache_mcastonly <0 | 1>
By default this switch is on.
It forces the cache to filter out
unicast packets.
Only broadcast or multicast packets are accepted.
machdep.wl_wlcache_iponly <0 | 1>
By default this switch is on.
It forces the driver to discard non-IP
packets and also stores the IP src address.
ARP packets are ignored,
as are any other network protocol barring IPv4 packets.
CAVEATS
The 82586 has numerous defects.
It may experience transmit-side
errors when modern faster cpus send packets at it faster than it can handle.
The driver (and probably the chip) does not support an all multicast mode.
As a result, it can be used with applications like
mrouted(8)PqPaports/net/mrouted,
but it must go into promiscuous mode for that to work.
The driver
is slow to change modes from "normal" to promiscuous mode, presumably
due to delays in the configuration code.
The
driver was written by
An Anders Klemets
(thousands of years ago?) and
appears to be based on an even older Intel 82586 driver.
The 82586
controller was one of the first (if not the first?) integrated lan
controller on the block.
That does not mean it was the best either.
Anders ported and or created a driver for the ISA wavelan and PCCARD
wavelan system too (wlp).
An Robert T. Morris, Jr.
ported the Mach drivers to BSDI.
An Jim Binkley
ported them to
Fx 2.1 .
An Michael Smith
ported the wl driver only to 2.2.2.
Jim and Michael have been
maintaining them.
The current state of the driver is NOT ANYONE'S
FAULT.
Thanks to
An Bernie Doehner
and
An Robert Buaas
for contributions.
