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. > > > > The changed value of MRVDRV_NF_DEFAULT_SCAN_VALUE is only used to > > magically conjure the missing noise value for scan results, see > > my other mail about this. > > > > Okay, it's also used in the case of a failed GET_RSSI command :-) > > > > > Well, when we had the (badly) averaged array values in there, > > > the noise floor was available to the scan reporting. > > > > Something might have been available for scan reporting, but if > > this "something" made sense is a different question. See my > > other mail :-) > > > > > There are tables to map RSSI -> dBm for each part which should > > > be in the firmware spec or seen in the driver code. > > > > 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: > • RSSI can be derived by adding Noise Floor to SNR value > • Noise Floor is returned in each received packet through the NF field > in the Rx Descriptor (dBm). > • 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 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. For further information, see something like: http://www.wildpackets.com/elements/whitepapers/Converting_Signal_Strength.pdf Dan -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
