Installing a TP-Link TL-WN722N (Atheros AR9721 802.11n) wireless dongle into Debian 6

My stock command-line Debian 6 (squeeze) install needs a few additional packages to handle a wireless dongle.

According to the Debian wiki, this chipset requires the firmware-atheros package, which is non-free.

Also the kernel needs to be 2.6.39 or higher...so stock squeeze (2.6.32) won't work, but the version in squeeze-backports (2.6.39) will work. Alternately, I could upgrade to Wheezy (the future Debian 7.0) or roll-my-own kernel.

Edit /etc/apt/sources.list to add the non-free archive and backports.

deb http://ftp.us.debian.org/debian/ squeeze main non-free
deb http://security.debian.org/ squeeze/updates main non-free
deb http://ftp.us.debian.org/debian/ squeeze-updates main non-free
deb http://backports.debian.org/debian-backports squeeze-backports main non-free

Begin using non-free and backports by updating the package cache:

# apt-get update

Install the packages needed to get wireless working in general, and this dongle in particular:

# apt-get install wireless-tools usbutils firmware-atheros

For backported packages, must specify. Use the Debian package search tool to locate the correct package name in the backport archive. For my 486-compatible system, it's:

# apt-get -t squeeze-backports install linux-image-2.6.39-bpo.2-486

Finally, create a wireless interface entry in /etc/network/interfaces

# The wireless interface
auto wlan0
iface wlan0 inet dhcp
    wireless-essid YourNetwork
    wireless-mode Managed

Since I use the syslinux bootloader (instead of grub) to get around the limitations of my 10-year-old motherboard, the new /boot/initrd.img generated by the new kernel must be manually copied over to my /boot partition. The following commands are specific to my setup only! IGNORE THIS SECTION IF YOU USE GRUB!

Remove unused grub stuff:

rm -r /boot/grub
rm /boot/System.map-2.6.39-bpo.2-486
rm /boot/config-2.6.39-bpo.2-486

Backup the old bootables:

# mv /boot/vmlinuz /boot/vmlinuz.old
# mv /boot/initrd.img /boot/initrd.old

Change the name of the new bootlables to 8-and-3 compatible so syslinux can use them:

mv /boot/initrd.img-2.6.39-bpo.2-486 /boot/initrd.img
mv /boot/vmlinuz-2.6.39-bpo.2-486 /boot/vmlinuz

Reboot, and suddenly the wireless works...until a bug or two intercede.

The dongle keeps crashing due to a possible kernel bug (or perhaps several). Interestingly, I also seemed to have two dhclient processes running. So lots of narrowing down to do...

1) Two dhclient processes upon boot (killed one manually)
2) Kernel bug that kills the dongle with dmesg: phy0: wlan0: No probe response from AP
3) Kernel or crda bug that thinks I'm in China (CN) instead of the US (US). The preferred fix is to install the crda package (not available for Debian 6.0). Alternate fix is to add a file /etc/modprobe.d/regdom.conf, containing the line options cfg80211 ieee80211_regdom=US (source)

Let's reboot.

Aha. After a reboot, ps -e | grep dh shows two dhclient processes. I killed the higher-numbered (later-started) one...which killed both of them and respawned a fresh dhclient process. So there's a bug: dhclient is getting spawned twice upon boot. But it's not related to the crash - that's a separate bug....