Hey Adrian, thanks a lot for your update! On Fri, Feb 01, 2013 at 11:02:00AM -0800, Adrian Chadd wrote: > Hi all, > > I've been tinkering with the HT40 spectral scan data (in FreeBSD, > obviously :-) and I can finally state that I have it working and > working reliably. > > The notes: > > * The "MAC does silly things to the spectral scan payload" problem > there is in HT40 too, so you need similar correction code for that. > I've not yet committed that to FreeBSD, but I will soon. > * The HT40 lower and upper FFT bins in the radar / spectral scan are > just that - lower and upper halves of a 40MHz wide FFT. > * .. but the RSSI in the RX descriptor is Primary and Extension > channel RSSI, so you need to match them up correctly with what's > "lower" and "upper" - ie, in HT40- mode, the primary RSSI is the > upper, and the extension RSSI is lower. > * .. and yes, this means you calculate the bin power separately for > the lower and upper bins. > * On AR928x chips, the spectral scan FFT is done on chain 0. I don't > think that's changed in AR93xx series chips. So, use RSSI and NF from > chain 0, don't use the combined RSSI figures. Ah, OK, that's probably relevant for the ath9k part as well. > * RSSI can be below 0 dB, so make sure you factor that in. > * IIRC, RSSI from the RX header is in half-dB increments, so make sure > you factor that in. > * Because of the MAC corruption bug, you can't disable "short report" > - otherwise you don't know whether the spectral scan data results are > corrupted or not. So yes, you have to enable short report and thus you > get one result at a time in a PHY error. Could we (in theory) enable short report stuff for newer chipsets, e.g. 93xx and newer? I thought there was a fix for that in "latest silicon", although I don't know specifics > > I've mostly working code in FreeBSD's subversion tree - > http://svn.freebsd.org/base/user/adrian/ath_radar_stuff/ - look in > lib/libradarpkt and src/fft_eval . > > I've begun fleshing out some documentation about spectral scan - > https://wiki.freebsd.org/dev/ath_hal%284%29/SpectralScan Excellent! That's provides a good resource. :) > > I'm going to work on the invalid packet length detection and > correction, based on what our reference driver does and what Zefir has > done. But once that's done, the basic data parsing and power > calculation bits are done - I'll work on exporting it in a > jquery-compatible fashion over a network socket so people (read: not > me :-) can write some visualisation apps using HTML/javascript. That > way both Linux and FreeBSD (and whoever else!) wifi hackers can > leverage the same visualisation apps when hacking on this stuff. Again, thanks a lot for your work! I'm currently busy with a few other things and probably won't find time to work on the 40 MHz spectral in the next weeks, so if anyone else wants to pick up here - the code has been prepared for that. :) In any case, please keep us posted, and keep up your good work! Thanks, Simon
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