Location reporting

This is an old revision of the document!

The AR9380 and later devices support a “time of flight” feature which can be used to estimate the distance between devices.

This is in note form for now!

there's a separate location timer register and control register
the counter is fed from the mac clock, so 44MHz in 20MHz wide operation, and 88MHz in 40MHz operation
a specific bit is set for a TX frame, which causes the full packet exchange to be returned
right now the only way to get the location timestamp is to enable the location timer, which causes /all/ frames to be timestamped with the location timestamp - ie, the TX/RX descriptor timestamps are no longer TSF.

The normal way this happens is:

fire off a TX frame with location_mode=1, not_sounding=0
get an RX frame (ACK) with the more bit set
.. and the second frame in the set is the sounding data with the rate, timestamp, etc and the payload is the CSI.

Overview