Wifi cards require firmware, i.e., code executed on the card's processor (not
on the main processor). Every Wifi chipset needs a different firmware.
Nowadays, this firmware usually is in the kernel and uploaded to the Wifi
card. Like any software, this firmware ought to be free. Unfortunately,
Linus Torvalds accepts proprietary firmware (blobs) in Linux. As a
consequence, constructors seize the opportunity to abuse users. It even is
probable that such blobs include malware. Spyware for instance. Of course,
the Trisquel project rejects proprietary firmware and the kernels it
distributes do not include these blobs. The related chipsets do not work.
Nowadays, only a few Wifi chipsets have free firmware. AR9170, AR9270 and
AR9271 are the ones you may encounter. The firmware named "ath9k_htc"
supports them. It was freed thanks to Chris' advocacy (Trisquel user and
ThinkPenguin's CEO). So the situation is worse than
"almost-everything-except-Atheros" fails to work in freedom because not all
Atheros chipsets have free firmware.
To make things worse, it is hard to know the chipset a model has.
Constructors do not write it on the wrapping... because they sometimes change
it, i.e., a Wifi card may work when another card of the same model (but
produced earlier or later) may not. So, either you acquire a card that has
been recently said to work in freedom (like Diomede's) and hope that the
chipset has not changed since then (the risk is little but exists) or you buy
from http://libre.thinkpenguin.com or http://tehnoetic.com (the only two
vendors that guarantee that their hardware works in complete freedom). The
second-hand market is a possibility too. If the vendor indicates the
chipset, for instance by showing the output of 'lsusb'.
By tomorrow, you may find the model Diomede suggests in a physical store.
You can bet on the TL-WN722N by TP-LINK too.
https://trisquel.info/forum/moving-trisquel indicates it included the AR9271
chipset in December. I bought four or five cards of that model years ago (it
had the same chipset). In this way, I can give/sell some to users of
computers I free with Trisquel.
