The Atheros HAL was reverse engineered for OpenBSD. adrian@freebsd used to work at Atheros and managed to get them to open source their HAL. The code is now in

The Atheros HAL was reverse engineered for OpenBSD. adrian@freebsd used to work at Atheros and managed to get them to open source their HAL. The code is now in FreeBSD where the HAL was a blob for years. AFAIK no hardware docs are available for people outside the company. Ralink used to provide documentation on request. They've been acquired by Mediatek since. Mediatek allows OpenBSD to distribute binary firmware images under free terms (for the run(4) driver). Perhaps they'd still provide docs. I haven't asked yet. Realtek's engineers tend to be kind and helpful, but they don't provide docs on request, citing NDAs, and management has ignored my requests. There are several open source drivers for Linux written by Realtek engineers which can be used as a reference but they are pretty large so studying them takes time. Broadcom's open source drivers are unreadable to the point of being more or less equivalent to binary blobs. If you want to see why try to make sense of this file in Linux: drivers/netwireless/brcm80211/brcmsmac/phy/phy_n.c