[ath9k-devel] how to config AR9280 for operation as 1X1 or other ideas

[Felix Fietkau <nbd@openwrt.org>]

On 2011-03-29 3:33 PM, Larry Vaden wrote:
> Good morning, ath9k devs and OpenWrt-users.
>
> Please excuse the cross post, not something we normally do.
>
> We have a particularly difficult situation in which we are trying to
> achieve a stable link over 1.2 miles with the Ubiquiti M900 which uses
> the AR9280 and thus 2X2 MIMO.
>
> We loaded OpenWrt trunk as a scientific control when we observed
> spontaneous reboots on AirOS 5.2.1 and 5.3.
>
> There is only one tree in the Fresnel zone and it has few leaves this
> time of year.  An unlicensed SCADA operation is a few miles away,
> using omnis at six water towers.
>
> To try to reduce the number of variables, we note with interest
> MikroTik's statement below the sig and ask folks on ath9k-devel and
> OpenWrt-users how to configure, e.g., OpenWrt to use only chain 0.
>
> Excerpts of dmesg for the AP are also below the sig.  dmesg on the CPE is quiet.
>
> If the objective of this email is unrelated, please offer any advice
> to achieve desired operation.
>
> THANKS in advance for your help --- it is fully appreciated.
To change the chainmask:

wifi down
echo 1 > /sys/kernel/debug/ieee80211/phy0/ath9k/rx_chainmask
echo 1 > /sys/kernel/debug/ieee80211/phy0/ath9k/tx_chainmask
wifi

This might have some side effects as the HT capabilities are not 
recalculated (ath9k does not support the antenna control API yet), but 
it will configure the PHY to only use one chain, and the rate control is 
usually able to deal with that just fine.

In order to debug this properly, please send a dump of the rate control 
stats of both sides:
cat /sys/kernel/debug/ieee80211/phy0/netdev:wlan0/stations/*/rc_stats

And also a dump of the channel busy time:
iw wlan0 survey dump

This might help narrow down the cause of this issue.

- Felix