From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: multi-antenna handling Date: Wed, 25 Jun 2014 09:04:49 +0200 Message-ID: <1403679889.4140.2.camel@jlt4.sipsolutions.net> References: <1345481425.4459.46.camel@jlt3.sipsolutions.net> <1373273952.8312.7.camel@jlt4.sipsolutions.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: Guy Harris , Felix Fietkau Cc: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org" List-Id: radiotap@radiotap.org On Tue, 2014-06-24 at 18:53 -0700, Guy Harris wrote: > > FWIW, I've now implemented this in Linux (in mac80211), although I start > > a new radiotap namespace for each antenna, separate from the first one, > > so you'll see > > > > * any of: TSF, flags, rate, channel, MCS, a-mpdu, VHT, ... > > (new radiotap namespace) > > * ant signal: -40 dBm > > * anntenna: 0 > > (new radiotap namespace) > > * ant signal: -45 dBm > > * anntenna: 1 > > ... for however many antennas/chains there are. > > So is the idea that, in the first radiotap-namespace block, there will > be no per-antenna information such as the antenna signal - the only > per-antenna information will be in the subsequent namespace blocks? Exactly. It would have seemed strange to include the per-antenna fields in general since the other data isn't specific to an antenna. It also shows nicer in wireshark this way :) > Context: somebody asked on ask.wireshark.org about a capture from a > D-Link router running OpenWRT; he claims that the router has 2 > antennas, but the capture has 3 antenna signal strength values, the > first of which is in the first radiotap namespace: > > http://ask.wireshark.org/questions/33994/why-there-are-3-rssi-values-in-the-radiotap-header-for-a-dual-antenna-wireless-card That's a bit strange - might be a driver quirk. The code I wrote has to rely on the driver, adding Felix who might know more, I don't know how ath9k works in this regard. johannes