dekstop: weblog

The following text explains how to get the Linksys WUSB11 2.8 working on OS X, and probably any other wifi adapter based on an Atmel AT76c505 chipset. (Caveat: As far as I know Kismac still does not support Atmel devices.)

Short version for people who have patched wifi drivers before: try the XTerasys XN-2122B drivers linked below. (mailtomomo indicates that AIN's AWU2000B also has a driver for OS X, and they do indeed have a download labeled "Mac driver", but that only links to an .exe)

Skip the prelude if you only want the raw facts.

Prelude

London has a lot of open wifi networks, so it's a paradise for the alyways-stay-connected junkie... Unfortunately my Powerbook's wifi antenna isn't too strong, which means it's usually a hassle to get a decent and stable connection. After one too many times of such technology-induced frustrations I decided I needed a remedy, so I bought a cheap external 802.11b USB adapter, the Linksys WUSB11 v2.8.

Unfortunately setting up the device turned out to be a pain -- I had consulted several hardware lists that uniformly declared WUSB11 v2.5 and v3 to be based on a Prism2 chipset, and I assumed that the v2.8 would certainly have the same technological basis; after all, 2.8 is in between 2.5 and 3, right? Needless to say, hardware manufacturers will disagree with that. After much experimentation with modified Prism drivers I finally opened the device and found an Atmel chip inside, the AT76c505. And as every wifi FAQ will tell you, Atmel and OS X == usually a bad match.

Long story short, the at76c503a driver project has a detailed list of AT76c50x wifi devices, which includes several devices based on the AT76c505, so I simply tried to find OS X drivers for every device listen on that page.

Howto

If you've never patched a driver before it may be helpful to check out the OS X wifi driver patching howto on mcquitty.net -- it's for a different chipset, but the overall approach is the same.

Step-by-step:

• Get your device's vendor and product ID from System Profiler (mine: vendor=0x1915, product=0x2233)
• If they're in hex: convert to decimal, e.g. with Calculator (mine: vendor=6421, product=8755)
• Download the OS X driver for the XTerasys XN-2122B USB stick
• it comes with three versions of the driver and configuration application (10.1, 10.2 and 10.3) -- I used the 10.3 versions
• open the DriverSetup.pkg bundle of your driver, open the Contents folder in Terminal, then run gunzip Archive.pax.gz
• open Archive.pax in a hex editor of your choice -- I use Hex Fiend
• search for the first occurrence of idProduct, replace the numeric value with the decimal product ID of your adapter; make sure not to change the overall file length (this is a binary file!) -- e.g. pad with zeros if your ID is shorter
• do the same for the first occurrence of idVendor
• re-pack the file with gzip Archive.pax
• now you can install your patched driver
• after rebooting go to System Preferences, open the Network panel, you should get a "new device found" message
• install XTerasys' config application (a rudimentary setup tool called WatlanX) and run it to connect to your network

Links

• xterasys.com: XTerasys XN-2122B OS Xdriver, product page
• berlios.de: AT76c50x-based wifi devices
• mcquitty.net: Patching OS X wifi drivers