Re: [RFCv2] Add spectral scan support for Atheros AR92xx/AR93xx

[Simon Wunderlich <simon.wunderlich@s2003.tu-chemnitz.de>]

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Hello Adrian,

thank you for posting this and the explanation!

On Sat, Dec 15, 2012 at 08:06:47PM -0800, Adrian Chadd wrote:
> The formats are as follows. Please note that if a pulse terminates
> during an FFT, the final entry may be truncated. So yes, you may not
> always get an integer multiple of the relevant frame length.

OK - my data is mostly in the range of 55-58 bytes (see below), sometimes
I got some longer packets, but I'm currently dropping them. 
The variation still puzzles me though.

> 
> Note that you shift each of the readings by max_exp to get a total
> reading. max_index and max_magnitude I think are just derived from the
> existing dataset; they're just a shortcut for software so it doesn't
> have to parse the whole frame looking for the peak.

Ah ok, that makes sense. Thanks for the clarification. :)
> 
> Static 20 mode:
> 
> 0  bin -28 magnitude[7:0] = (|i| + |q|) >> max_exp
> 1  bin -27 magnitude[7:0] = (|i| + |q|) >> max_exp
> 2 - 53  …
> 54  bin  26 magnitude[7:0] = (|i| + |q|) >> max_exp
> 55  bin  27 magnitude[7:0] = (|i| + |q|) >> max_exp

I've checked my data again: On my AR9280 in 2.4GHz, I get 55 or 57 bytes plus
7 "special bytes" (4 bytes meta info plus 3 bytes "radar trailer?"). In 5 GHz
and on my AR9380 in both bands, it is always either 56 or 58 bytes. The number
of bytes comes from rs_datalen from the rx_status struct as found in the patch
sent earlier.

So to summarise, what I currently get:
 * 55-58 bytes of "data"
 * 4 bytes of meta-information (as you provided)
 * 3 bytes of "radar trailer" (bwinfo and such)

The variation in the data puzzles me, I've already checked bit 4 in bwinfo
as Felix suggested. Is there any other "header" to the DFS data? Or should I
just skip the first few bytes and always use the last 55 bytes? At least from the
distribution, all of these numbers look like normal data and not a bitfield.
Ideas welcome. :)

I've also noticed that the middle of the data (like data[28]) is usually higher
than the rest - this might be the carrier, or something alike?

> 56  [7:0]: all bins {max_magnitude[1:0], bitmap_weight[5:0]}
> 57  [7:0]: all bins  max_magnitude[9:2]
> 58  [7:0]: all bins {max_index[5:0], max_magnitude[11:10]}
> 59  [3:0]: max_exp (shift amount to size max bin to 8-bit unsigned)
> 
> Dynamic 20/40 mode:
> 
> 0  bin -64 magnitude[7:0] = (|i| + |q|) >> max_exp  or  power (in dBm)
> 1  bin -63 magnitude[7:0] = (|i| + |q|) >> max_exp  or  power (in dBm)
> 2 - 125  …
> 126  bin  62 magnitude[7:0] = (|i| + |q|) >> max_exp  or  power (in dBm)
> 127  bin  63 magnitude[7:0] = (|i| + |q|) >> max_exp  or  power (in dBm)
> 128  [7:0]: lower bins {max_magnitude[1:0], bitmap_weight[5:0]}
> Baseband DFS 2 (Radar) Micro-Architecture
> 129  [7:0]: lower bins  max_magnitude[9:2]
> 130  [7:0]: lower bins {max_index[5:0], max_magnitude[11:10]}
> 131  [7:0]: upper bins {max_magnitude[1:0], bitmap_weight[5:0]}
> 132  [7:0]: upper bins  max_magnitude[9:2]
> 133  [7:0]: upper bins {max_index[5:0], max_magnitude[11:10]}
> 134  [3:0]: max_exp (shift amount to size max bin to 8-bit unsigned)

Thanks again, also for posting the radar packet format! I'll play a little bit more
with spectral for now ...

Cheers,
	Simon

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