Return-path: Received: from mail30g.wh2.ocn.ne.jp ([220.111.41.239]:31679 "HELO mail30g.wh2.ocn.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1757845AbYDCCFV (ORCPT ); Wed, 2 Apr 2008 22:05:21 -0400 From: bruno randolf To: "Luis R. Rodriguez" , Ulrich Kunitz , Daniel Drake Subject: Re: [PATCH] mac80211: use hardware flags for signal/noise units Date: Thu, 3 Apr 2008 11:05:05 +0900 Cc: ath5k-devel@lists.ath5k.org, jirislaby@gmail.com, mickflemm@gmail.com, linux-wireless@vger.kernel.org, linville@tuxdriver.com, johannes@sipsolutions.net, flamingice@sourmilk.net, jbenc@suse.cz, "Ivan Seskar" , "Jean Tourrilhes" , "Haris Kremo" , "Ivo van Doorn" References: <20080326123042.11233.80949.stgit@localhost> <200803271107.54208.bruno@thinktube.com> <43e72e890804021227y520380f7j8ad25eb30f635d2b@mail.gmail.com> In-Reply-To: <43e72e890804021227y520380f7j8ad25eb30f635d2b@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Message-Id: <200804031105.06176.bruno@thinktube.com> (sfid-20080403_030526_206427_6CE96C2F) Sender: linux-wireless-owner@vger.kernel.org List-ID: On Thursday 03 April 2008 04:27:31 Luis R. Rodriguez wrote: > > so in the "unspecified" case we really don't know much about the units, > > in the worst case we can't even assume that 1/2 the value will mean 1/2 > > of the received signal strength. it's very hard to work with this values, > > but it's better than nothing. > > > > other cards might not have noise, so no absolute (dBm) measurement, but > > a form of RSSI which is measured in dB (that is a logarithmic > > difference). in this case we might not know which reference point the > > measurement is taken to, but we know how it behaves: -3 dB means half of > > the signal strength. if you add a 6dB gain antenna you can expect to see > > the signal reading to increase by 6dB. it's not strictly SNR (because we > > don't know the noise) but quite close to it. > > > > i think it's important to know the difference between this 3 cases i > > order to make some sense of the values in userspace gui, roaming agents, > > mesh link metrics, etc... > > Agreed, but can you give me an example of a card which does provide > RSSI in db for values we don't know and that UNSPEC cannot handle? Is > this what is assumed of the rt2x00 cards? i currently assume that for rt2x00 and zd1211 cards - but i'm really just guessing here. feedback from driver authors or people who have more knowledge about the hardware would be greatly appreciated! here's the current table: DRIVER SIGNAL MAX NOISE QUAL ----------------------------------------------------------------- adm8211 unspec(?) 100 n/a missing at76_usb unspec(?) (?) unused missing ath5k dBm dBm percent rssi b43legacy dBm dBm percent jssi(?) b43 dBm dBm percent jssi(?) iwl-3945 dBm dBm percent snr+more iwl-4965 dBm dBm percent snr+more p54 unspec 127 n/a missing rt2x00 percent rssi+tx/rx frame success rt2400 dB(?) 100 n/a rt2500pci dB(?) 100 n/a rt2500usb dB(?) 100 n/a rt61pci dB(?) 100 n/a rt73usb dB(?) 100 n/a rtl8180 unspec(?) 65 n/a (?) rtl8187 unspec(?) 65 (?) noise(?) zd1211 dB(?) 100 n/a percent bruno