Wednesday, November 16, 2011

FreeBSD is now doing (even more) 802.11n..

I held off merging in my 802.11n work as much as possible but I decided that I'd like to get it done before the end of the year. Even though 9.0-RELEASE is still around the corner, I decided that it would be better to merge in what I have into -HEAD and then tidy that up then wait for what could be a few more months.

So, it's in there, bugs and all, supporting both station and hostap mode. No, wds, adhoc, mesh and TDMA aren't currently supported (I have enough bugs to worry about for the time being, without trying to debug the other operating modes. But I'd like to.)

What works:
  • TX and RX aggregation!
  • The rest of the 802.11n negotiation stuff, mostly thanks to Bernhard Schmidt who fixed up a lot of the net80211 quirks.
  • Lots of ANI changes which hopefully make noisy environments more stable.

What doesn't yet work:

  • Interface resets cause frames to be dropped from the RX and TX queues. This messes up aggregation and causes sessions to hang. I'm fixing that up in a git branch at the moment.
  • BAR TX - I'll implement BAR TX soon - it's just tricky to get right.
  • Filtered frames - ie, TX failed frames from the hardware. Instead of the current method of "always try", the hardware supports failing the current and subsequent frames in a set. That way a hostap seeing a station going into power saving mode can quickly abort all TX frames to said station and then only retransmit them when the station indicates it's again awake. If I don't do this then the hardware will constantly fail a lot of frames, causing BAR frames to be TXed when they likely shouldn't be.

But it's enough to try. So if you have an AR5416, AR9160, AR9220, AR9280, AR9285, AR9227 or AR9287, give it a whirl. If you have a pre-11n NIC then please, give it a go too. I'd like to ensure that the hardware support for earlier chipsets hasn't broken.

If you'd like to use this in production on a hostap then please keep in mind that power saving support isn't entirely functional and featured, so stations which go into frequent power saving mode may have some performance issues. I'll tinker with this some more soon.

Finally, thank you very much to Hobnob, Inc. for sponsoring this work and Qualcomm Atheros for providing me source code, documentation and assistance in understanding how all of this works.


  1. This is very very good. Fantastic job.
    Have some way to downgrade to 8.2 ? I try to do like explained here:, however, i have the same error reported by palochka.

    Congratulations for this great work.

  2. Do you implement software AMPDU TX function? I download codes from but only a complete AMPDU TX function is implemented in net80211.
    I want to test the function in FreeBSD? Is it finished?

  3. Hi!

    Yes, AMPDU-TX is supported. It's not power save aware yet but the rest is supported (ie software retransmission, BAR TX, etc.)