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ATW(4) NetBSD Kernel Interfaces Manual ATW(4)
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atw -- ADMtek ADM8211 802.11 wireless network driver
atw* at cardbus? function ?
atw* at pci? dev ? function ?
The atw driver supports PCI/CardBus 802.11b wireless adapters based on
the ADMtek ADM8211.
The ADM8211 is a bus-mastering 802.11 Media Access Controller (MAC) which
is derived from ADMtek's Tulip clones (see tlp(4)). It supports con-
tention-free traffic (with an 802.11 Point Coordinator), 64/128-bit WEP
encryption, and 802.11 power-saving. The ADM8211 integrates an RF3000
baseband processor (BBP) by RF Microdevices.
In a typical application, the ADM8211 is coupled with an RF front-end by
RFMD and a Silicon Laboratories Si4126 RF/IF synthesizer.
With the ADM8211, the division of labor between the host and NIC is dif-
ferent than with firmware-based NICs such as an(4), awi(4), and wi(4).
The ADM8211 is still responsible for real-time 802.11 functions such as
sending ACK/RTS/CTS/ATIM frames, sending beacons, and answering CF polls
from the access point, but the host takes responsibility for providing
802.11 functions such as scanning, association, and authentication. The
host is also responsible for programming both the BBP and the RF/IF syn-
atw contains incomplete support for the ADM8211's WEP encryption/decryp-
tion engine. atw does not yet support hardware WEP decryption, however,
it will use the ADM8211's crypto engine to encrypt transmitted frames.
Documentation from ADMtek claims that, in addition to the 4 128-bit
shared WEP keys, the ADM8211 will store WEP key pairs for up to 20 peers.
The documentation provides no details, hence atw does not support the 20
The ADM8211 operates in 802.11 infrastructure mode (with an access point)
and in 802.11 ad hoc mode (without an access point) at 1, 2, 5.5, and
11Mbps. ADMtek says that the ADM8211 cannot operate as an access point.
The operating mode is selected using the ifconfig(8) utility. For more
information on configuring this device, see ifconfig(8) and ifmedia(4).
Cards supported by the atw driver include:
D-Link DWL-650 Rev. ?? CardBus card
D-Link DWL-520 Rev. C1 PCI card
LanReady WP2000 PCI card
TrendNet TEW-221PC CardBus card
Xterasys XN2511B PCI card
atw0: failed to tune channel %d The driver failed to tune the radio to a
new channel. The radio remains tuned to the old channel.
atw0: atw_si4136_write wrote %08x, SYNCTL still busy The driver waited
100ms without seeing an indication that the ADM8211 had finished writing
a register on the Si4126 RF/IF synthesizer.
atw0: device timeout The ADM8211 failed to generate an interrupt to
acknowledge a transmit command.
arp(4), cardbus(4), ifmedia(4), netintro(4), pci(4), ifconfig(8)
Silicon Laboratories, http://www.silabs.com.
RF Microdevicdes, http://www.rfmd.com.
The atw device driver first appeared in NetBSD 2.0.
The atw driver was written by David Young <dyoung@NetBSD.org>. For fea-
tures which the ADM8211 has in common with the DECchip 21x4x, code was
liberally borrowed from tlp(4) by Jason Thorpe <thorpej@NetBSD.org>.
The author does not fully understand what processing the duration fields
for the PLCP header and the 802.11 header undergo before they are applied
to a transmitted frame. If the duration fields in transmitted frames are
incorrect, the performance of your network may suffer.
The driver does not provide rate control when the media type is set to
The driver lets you change to hostap mode, but it does not work and it
probably never will.
The driver will sometimes complain that it cannot re-tune the radio
because the transmit process has not gone idle. The author is investi-
Many features are still missing, especially WEP decryption and 802.11
The ad hoc mode has not been rigorously tested. IBSSs with the same SSID
may not coalesce, but this should not matter for most applications.
The driver is untested in the ad-hoc demo mode of Lucent WaveLAN cards.
The ADM8211 supports 802.11 power-saving, however, atw does not support
it yet. For time-bounded service, the ADM8211 will interoperate with an
access point which implements the 802.11 Point Coordination Function,
however, this is also not supported.
Combinations of an ADM8211 with either an Intersil or a Marvell RF front-
end are not supported.
NetBSD 4.0 June 5, 2004 NetBSD 4.0