Madwifi regdomain issues

The CS Department at UCT has some Wireless APs on Channel 13. This is quite cool (for geeky reasons), but my MacBook (purchased in the US) did not agree. As far as it is concerned, the only 802.11g channels in existence are 1-11.

The reason for this is that my Atheros (madwifi) network card is a software-defined radio. Atheros interprets the FCC regulations to mean that it cannot provide an Open Source driver for this card, allowing it broadcast on any random channel. Thus the madwifi driver contains a binary HAL, produced by Atheros, which is responsible for regulating frequencies and power levels. (This HAL has been reverse-engineered by the OpenBSD people, but not for my card, unfortunately).

The card has two values stored in it’s EEPROM, a “countrycode”, and a “regdomain”. The countrycode is overrideable in software (you modprobe ath_pci countrycode=710), but only if the countrycode you specify is valid for the card’s regdomain. Some cards have a 0x00 or 0xFF regdomain (wildcard values), but mine had 0x64. This meant that whenever I tried to specify a country code, I’d get an error, and the madwifi module would refuse to load:

Feb 11 11:34:11 beethoven kernel: [ 2047.669023] MadWifi: ath_getchannels: Unable to collect channel list from HAL; regdomain likely 100 country code 710

There has been some success with changing the regdomain in the EEPROM, using the hard-to-find ar5k utility (or possible the ath_info utility?). However, again this didn’t work with my model. But I found an e-mail from somebody who’d been playing with similar stuff. I mailed Salvatore, and he replied almost instantly, pointing me to a public Windows utility for changing regdomains. It depends on a special driver, available in the demo of “CommView for Wireless”.

I installed Windows in my swap partition (it’s not an operating system I normally have around). (Naturally, I forgot to have an Ubuntu CD handy, to rebuild my grub, but that was easily remedied.). After a few blue screens of death (install all necessary drivers first), I got my regdomain changed to 0x37, which is the regdomain for South Africa & Europe.

Now, I’m writing this from a couch in the CS department, using a channel 13 AP. Success.

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