[ath9k-devel] ath9k: spectral scan -vs- channel state information

On 12 April 2016 at 15:05, Dan <[email protected]> wrote:
> Hi
>
> I am having some trouble understanding the difference between
> channel state information (often requested on the mailing list)
>  and what is currently available via spectral scan.
>
>
> My understanding is as follows;
> - spectral scan (once triggered via the debugfs) logs
> channel state estimation for each of the 56 ofdm subcarriers
>  (HT20 case). In the spectral code (for ath9k), the channel state
> info is the I and Q values for the subcarriers.
> For ath9k, the bulk of the code is in ath_process_fft

Right. And it's sent over as a PHY error frame.

> Bits I dont understand :
> Can channel state information be collected on a more general
> basis ? --- for example for each phy packet received.

No. There's not enough bandwidth available in the PHY->MAC connection
to also throw over that much data per packet. So, you get to trigger
it once, and then the next packet gets the CSI data dumped into a
memory region in the chip somewhere. Then you read it out.

> Also, the calibration (ar9003_calib) seems to gather I and Q
> data also... but its not clear when this is run/collected and used.

> Any help appreciated....

That's part of ADC calibration. The idea is to calibrate differences
in ADCs on the I and Q side of things.



-adrian