Sam Leffler, maintainer of the binary HAL that is also used in MadWifi releases, has released the source code for his HAL variant under ISC license. It is available through a Subversion repository (web interface), which is also be used actively for development and further improvements.
In his announcement, Sam states:
Coincident with the release of this code I have concluded my agreement with Atheros whereby I had access to information about their devices. This means that in the future all fixes, updates for new chips, etc. will need to be a community effort. Atheros states the Linux platform will be the reference public code base so folks wanting to add support for other platforms will have to scrape the information from there.
“Linux platform” refers to ath5k and ath9k. Interested parties are advised to attend the ath5k-devel and ath9k-devel mailing lists. These lists may be also used to ask general questions about the chipsets supported by the respective drivers.
For Linux developers this means further access to documentation to help enhance drivers like ath5k in particular for the AR5210 and AR5211 family of chipsets. For the FreeBSD and NetBSD family this means a drop in open replacement for the binary HAL which was being used.
Source: http://madwifi-project.org/wiki/news/20081129/sam-leffler-releases-hal-source