[ath9k-devel] Realtime plot of Spectral Scan in ath9k

[Gui Iribarren <gui@altermundi.net>]

On 07/26/2013 01:18 PM, Gui Iribarren wrote:
> On 07/25/2013 04:54 PM, Adrian Chadd wrote:
>> Cool!
>>
>
> Gabriel Tolon has various measurement equipment, so i hope with this
> visualization he'll be able to better calibrate or find
> misintepretations of the source data :D

Ahh, already enjoying this! Baby steps so far, but already answering my 
own questions about why the data plots the way it is... :)

While trying to visualize a transfer on channel 1, i can see perfectly 
the "ladder" on neighbouring channels, but an unexplainable low sampling 
on the actual channel 1.
Turns out, the FFT is done only when the radio is idle; that is, not 
receiving or sending packets;
Felix told me about that back in April,
and Adrian clearly states in
https://wiki.freebsd.org/dev/ath_hal%284%29/SpectralScan
"either spectral scan FFT reporting can run, OR packet 
transmission/reception"
(+1 Insightful)

but seeing it live, is a whole another thing :D

http://tinypic.com/r/16bld2r/5

now it's pretty clear that when radio is tuned to (say) channel 2, it 
can't decode the packets and only sees a very intense "noise" (i.e part 
of the neighbouring transmission).
but when it's on channel 1, it can fully decode the packets (even though 
they're destinated for someone else) and during that time no FFTs are made.
So, what are the few samples you can see on channel 1?
Well, either A) silent instants along the transfer, or B) partial 
transmissions, but in terms of time; i.e. the radio tuned into 2412 in 
the middle of an ongoing packet, and since it lost half of it, can't 
decode it and samples the "tail" of the packet as a mildly intense "noise".

Cheers!