ath9k / ath9k_htc: strange behavior of the TSF value

[Robert Felten]

Hi Oleksij,

thanks for your fast reply. Indeed the strange behavior gone in
ath9k_htc fw v1.4.

Thanks! :)


BR
Robert


2016-02-18 16:19 GMT+01:00 Oleksij Rempel <linux at rempel-privat.de>:
> Hi Robert,
>
> Am 18.02.2016 um 16:00 schrieb Robert Felten:
>> Hi all,
>>
>> in my understanding, the TSF value is used to synchronize the medium
>> access in a BSS. Also my expectation the TSF value would just increase
>> monotonic (until rollover).
>>
>> But the TSF value (provided by the radiotap headers) shows a strange
>> behavior on my machine:
>> Sometimes the value increases a lot, and shortly after, in decreases
>> almost by the same amount.
>>
>> To understand this behavior, I set up my TL-WN722N (AR9271, ath9k_htc)
>> device in STA mode (connected it to an AP) and dumped ~200k packets in
>> Wireshark.
>> Then I extracted the of TSF the STA and the TSF in the of the beacon
>> frames via tshark:
>>
>>  $ tshark -nr dump.pcapng -T fields  -e frame.number -e
>> radiotap.mactime -e wlan_mgt.fixed.timestamp -R 'wlan.bssid == <AP's
>> MAC>  and wlan.fc.subtype == 8'"
>>
>> The AP's TSF shows the expected monotonic behavior, but the local STA
>> TSF "jumps" somehow, for instance on the frame # 121641 or 224784:
>>
>> Frame#   STA TSF                AP TSF
>> 121594    2160015947309    0x000000c7ec26f9b2
>> 121614    2160016082477    0x000000c7ec2889b1
>> 121626    2160016152108    0x000000c7ec2a19b2
>> 121641    2160032998968    0x000000c7ec2ba9bf   <-- STA TSF ???
>> 121657    2160016356907    0x000000c7ec2d39b4
>> 121684    2160016459308    0x000000c7ec2ec9b4
>> 121714    2160016594080    0x000000c7ec305828
>> ...
>> 224473    2160099843558    0x000000c7f126a380
>> 224550    2160099913188    0x000000c7f1283380
>> 224683    2160100015591    0x000000c7f129c380
>> 224784    2160368520676    0x000000c7f12b5380  <-- STA TSF ???
>> 224872    2160100222543    0x000000c7f12cebeb
>> 224890    2160100355555    0x000000c7f12e7380
>> 225252    2160100629986    0x000000c7f1332380
>> ...
>>
>> The STA TSF value only "jumps" on beacon packets (I tested w/o the
>> filter 'wlan.fc.subtype == 8' ) and the "jumps" differs a lot in
>> magnitude. I seems that the next beacon set the value back to an
>> expected value.
>>
>> I would be very happy if someone could versify / falsify of this
>> behavior on his/hers machine and/or point me to an explanation. :)
>>
>> My kernel is 3.19.0-49-generic #55~14.04.1-Ubuntu SMP and an ath9k_htc
>> based TL-WRN722N WiFi device. Further details of any level could be
>> provided on request.
>>
>
> There was a Firmware fix for this issue. It should be in FW version 1.4
> I assume you are using 1.3.
> Please update your kernel and FW.
>
> --
> Regards,
> Oleksij
>