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 S1755449AbYCSTnd (ORCPT ); Wed, 19 Mar 2008 15:43:33 -0400 Subject: Re: [RFC] libertas: change quality calculation From: Dan Williams To: Holger Schurig Cc: libertas-dev@lists.infradead.org, linux-wireless@vger.kernel.org In-Reply-To: <200803191625.39210.hs4233@mail.mn-solutions.de> References: <200803181510.52726.hs4233@mail.mn-solutions.de> <1205937928.26119.29.camel@localhost.localdomain> <200803191625.39210.hs4233@mail.mn-solutions.de> Content-Type: text/plain; charset=utf-8 Date: Wed, 19 Mar 2008 11:38:17 -0400 Message-Id: <1205941097.4169.23.camel@localhost.localdomain> (sfid-20080319_194535_522422_ED6140A7) Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: 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? See section 7.3 of the 5.1 spec: 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 the= NF field in the Rx Descriptor (dBm). =E2=80=A2 Signal Quality is determined by RSSI and SNR. Section 3.1 as well (Receive Packet Descriptor): "RSSI should be calculated in the driver as a summation of the SNR and NF" 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 b= y 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. 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