From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([66.187.233.31]:55887 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758092AbYCSTnW (ORCPT ); Wed, 19 Mar 2008 15:43:22 -0400 Subject: Re: [RFC] libertas: change quality calculation From: Dan Williams To: Holger Schurig Cc: linux-wireless@vger.kernel.org, libertas-dev@lists.infradead.org In-Reply-To: <1205941097.4169.23.camel@localhost.localdomain> References: <200803181510.52726.hs4233@mail.mn-solutions.de> <1205937928.26119.29.camel@localhost.localdomain> <200803191625.39210.hs4233@mail.mn-solutions.de> <1205941097.4169.23.camel@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Date: Wed, 19 Mar 2008 11:41:54 -0400 Message-Id: <1205941314.4169.31.camel@localhost.localdomain> (sfid-20080319_194521_612042_8846E04E) Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Wed, 2008-03-19 at 11:38 -0400, Dan Williams wrote: > On Wed, 2008-03-19 at 16:25 +0100, Holger Schurig wrote: > > > > I also found that the average noise floor is -86 dBm, not > > > > -96 dBm. So I changed this constant. Maybe this is wrong, > > > > what values do your cards report? > > > > > > When possible, we should use a window-ed average of the cards > > > reported noise from beacons or received frames instead of a > > > constant, that's a further improvement though. > >=20 > > The changed value of MRVDRV_NF_DEFAULT_SCAN_VALUE is only used to=20 > > magically conjure the missing noise value for scan results, see=20 > > my other mail about this. > >=20 > > Okay, it's also used in the case of a failed GET_RSSI command :-) > >=20 > > > Well, when we had the (badly) averaged array values in there, > > > the noise floor was available to the scan reporting. > >=20 > > Something might have been available for scan reporting, but if=20 > > this "something" made sense is a different question. See my=20 > > other mail :-) > >=20 > > > There are tables to map RSSI -> dBm for each part which should > > > be in the firmware spec or seen in the driver code. > >=20 > > I didn't see such a table so far, where is it? >=20 > See section 7.3 of the 5.1 spec: >=20 > 7.3 RSSI and Noise Floor Support > The firmware supports the reporting of RSSI and Noise Floor values: > =E2=80=A2 RSSI can be derived by adding Noise Floor to SNR value > =E2=80=A2 Noise Floor is returned in each received packet through t= he NF field > in the Rx Descriptor (dBm). > =E2=80=A2 Signal Quality is determined by RSSI and SNR. >=20 > Section 3.1 as well (Receive Packet Descriptor): >=20 > "RSSI should be calculated in the driver as a summation of the SNR an= d > NF" >=20 > So Marvell doesn't really provide a table, but we'll have to do some > investigation here. The RSSI is almost always a random value defined= by > the manufacturer [1] or in dBm. We're not 100% sure what Marvell is > using here, but some investigation will show whether the value is > actually in dBm or in some other units. A quick check of the RSSI > reported by the current BSS in scan results versus the output of > GET_RSSI might show something interesting. =46or further information, see something like: http://www.wildpackets.com/elements/whitepapers/Converting_Signal_Stren= gth.pdf Dan -- To unsubscribe from this list: send the line "unsubscribe linux-wireles= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html