[rt2x00-users] Low link quality / or disconnect after scan with RT3572 and Xirrus AP
ronald.wahl at raritan.com
Sat Mar 3 02:38:53 EST 2012
I have some strange issues with an RT3572 based WLAN USB Stick and my
Xirrus AP. Maybe one of you can help me debugging this:
Embedded platform using AT91SAM9G20
Full speed USB (i.e. 12 MBit USB link speed)
WLAN Stick is an ASUS USB N-53 based on Ralink RT3572
The AP is an Xirrus XN4.
The Linux kernel version is 3.2.5. I'm using the nl80211 API to access
the kernel in in wpa_supplicant.
The quality of the WLAN connection is initially usable (RSSI: -50db) and
after a scan it drops immediately to low values (RSSI: -75db or lower)
or the STA is disconnected altogether immediately. This happens in the
5GHz and the 2.4GHz bands. The 5GHz band tends to just drop the quality
and the 2.4GHz band often just disconnects but this is probably just a
minor detail. After the supplicant reconnects everything is back to
normal. Also if I restart the scan when quality is low the link quality
is back to normal during this scan but drops again after the scan
finishes. A precondition to this is some medium traffic on the
connection (in my case an snmp bulkwalk in an endless loop against the STA).
This issue happens only on my the embedded platform which is a lot
slower than a regular PC (even if I use an USB 1.1 hub to slow down the
USB link). I can reproduce this only with my Xirrus XN4 AP and not with
an Cisco Aironet 1142 AP.
Also the scan times are much longer on the embedded platform - for each
channel it takes almost a second to scan. So a full scan took 37 seconds.
For testing purposes I applied all the RT2X00 patches from wireless-next
branch before the VCO patches because there were some changes rearding
the RT3572 chip. But this did not change anything on the behavior.
I also tried using the wext driver instead og nl80211 in wpa_supplicant
but this does also not change anything.
An interesting observation might be also that it looks like that the
station does not send packets anymore to the AP because after some time
the station is disconnected by the AP because of inactivity and also the
bulkwalk that I have running does only timeout after the scan.
I suspect that because of the long scan time something times out and
some driver/chip state is not restored that is necessary for regular
operation. Might this be true?
Any ideas how to debug / fix this?
PS: I'm not in the list so keep me in Cc:, please. Thx!
Ronald Wahl - ronald.wahl at raritan.com - Phone +49 375271349-0 Fax -99
Raritan Deutschland GmbH, Kornmarkt 7, 08056 Zwickau, Germany
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Geschäftsführung: Stuart Hopper, Burkhard Wessler
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