Signal sensitivity problem with if_rum

[Paul B. Mahol]

On 5/1/09, Gustau Perez <gperez at entel.upc.edu> wrote:
>
>   Hi,
>
>   I think this is right place to post, if it is not, please let me know.
>
>    I'm experiencing problems with two different devices using if_rum.
> One is a Hercules Guillemot and the other is a Linksys Cisco WUSB54GC
>
>   The first one is about sensitivity, which is very low: for example,
> I'm detecting just two or three networks around me (with windows both
> usb devices detect around 14 or 15 networks) and the reported signal is
> very low.Placing the sensor very near to my wireless network AP (which
> is a FreeBSD machine with atheros card placing the txpower to 20)
> reports a signal quality of 50% or 60%.
>
>   Linux presents the same problem (my wife's laptop with ubuntu shows
> the same figures, more or
>
>   The other one is that having such a low sensitivity makes those
> dongles unusable when making large transfers, mostly when using scp/sftp
> or sshfs (samba seems to make it work better for longer transfer, but
> finally the problem appears). At some given point, the dongles seem to
> lose contact with the AP (making ifconfig shows that wlan0 is still
> associated), waiting for a period of time (usually one or two minutes)
> the transfer continues. Probably both problems are related.
>
>   In order to debug the problem I tried looking dmesg in both my AP and
> my laptop (no trace). Tried looking at the ssh logs (when making large
> transfers, no clue). In the only place I found something was in the
> samba logs, only saying that there was a problem with the transfer
> (broken pipe, the socket is closed).
>
>   So :
>
>   In the linux world, I found that the register which controls the
> sensitivity is bbp17 :
>
> http://209.85.229.132/search?q=cache:H8W6R5Ds3mYJ:forum.aircrack-ng.org/index.php%3Ftopic%3D2235.0+bbp17+ralink+linux&cd=1&hl=ca&ct=clnk&gl=es&client=firefox-a
>
>    Tried looking in
> /usr/src/sys/dev/usb/wlan/if_rum.c, but I got lost. Tried with sysctl -a
> | grep rum or grep wlan0, but no MiB related to sensitivity appeared.
>
>   Is there anything I can try ? How can I force bbp 17 to get 0 value ?
> Tried with rum_def_bbp in if_rum.c, changing 17 to 0. No luck.

There is several places where bbp17 is changed.

Last time I was exploring
rum I found that it lacks bbp auto tuning.
[Failed to implement it, because in meantime I broke chip :)]

-- 
Paul