ath_spectral
============
ath_spectral is a Qt-Qwt UI developed to draw FFT spectral samples gathered 
from Atheros NICs. AR92xx and AR93xx have the ability to report FFT data
from the baseband, including:
*) absolute magnitude (|i|+|q|, abs() for I/Q phase of the wireless signal)
   for each FFT bin (56 for subcarriers in HT20 mode and 128 in HT40 mode)
*) an index indicating the strongest FFT bin
*) the maximum signal magnitude for each sample

These information can be used to create an open source spectrum analyzer
or interference classifier

build
=====
Qt (>=5.0) should be installed on the system
Just type qmake and make to build the program
$ qmake
$ make
$ export LD_LIBRARY_PATH=${PWD}/qwt/lib/

This program has been tested using qwt-6.1.0 and qt-5.0.1

frame format
============
FFT dara is reported as PHY error:

*) HT20
 	0	1	2	3	4	5	6	7	8
 	+---------------------------------------------------------------+
 0	|	[7:0]: bin -28 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 1	|	[7:0]: bin -27 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 2-54	| 								|
 	+---------------------------------------------------------------+
 55	|	[7:0]: bin 27 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 56	|	[7:0]: all_bins {max_magnite[1:0], bitmap_weight[5:0]}	|
 	+---------------------------------------------------------------+
 57	|		[7:0]: all_bins {max_magnite[9:2]}		|
 	+---------------------------------------------------------------+
 58	|	[7:0]: all_bins {max_index[5:0], max_magnite[11:10]}	|
 	+---------------------------------------------------------------+
 59	|			[3:0] max_exp				|
 	+---------------------------------------------------------------+
   

*) HT40
 	0	1	2	3	4	5	6	7	8
 	+---------------------------------------------------------------+
 0	|	[7:0]: bin -64 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 1	|	[7:0]: bin -63 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 2-125	| 								|
 	+---------------------------------------------------------------+
 127	|	[7:0]: bin 63 magnitude (|i| + |q|) >> max_exp		|
 	+---------------------------------------------------------------+
 128	|    [7:0]: lower_bins {max_magnite[1:0], bitmap_weight[5:0]}	|
 	+---------------------------------------------------------------+
 129	|		[7:0]: lower_bins {max_magnite[9:2]}		|
 	+---------------------------------------------------------------+
 130	|	[7:0]: lower_bins {max_index[5:0], max_magnite[11:10]}	|
 	+---------------------------------------------------------------+
 131	|    [7:0]: upper_bins {max_magnite[1:0], bitmap_weight[5:0]}	|
 	+---------------------------------------------------------------+
 132	|		[7:0]: upper_bins {max_magnite[9:2]}		|
 	+---------------------------------------------------------------+
 133	|	[7:0]: upper_bins {max_index[5:0], max_magnite[11:10]}	|
 	+---------------------------------------------------------------+
 134	|			[3:0] max_exp				|
 	+---------------------------------------------------------------+

Riceved power computation
=========================
Assuming the noise floor is equal to -96dbm(*) and the magnitude of each sample
in a 20MHz bin equals the RSSI, the received signal strength of each FFT bin
can be computed as follow:

*) HT20
	power(i) = nf + RSSI + 10*log(b(i)^2) - bin_sum

where:
	- RSSI is computed on control chain 0
	- b(i) is the magnitude in each bin, unscaled by max_exp
	- bin_sum = 10*log(sum[i=1..56](b(i)^2)

*) HT40
for 40MHz channel, previous formula should be used for 64 bins of control and
extension channels, keeping in mind for HT40+ mode the extension channel is
above the primary one (lower=ctl, upper=ext) and for HT40- the extension
channel is below the primary one (lower=ext, upper=ctl)

(*) nf can differ from -96dbm due to noise and spikes leading to a reduced
reported RSSI

(this document is based on https://wiki.freebsd.org/dev/ath_hal%284%29/SpectralScan, thx :))