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Date: Wed, 24 Oct 2012 16:33:46 -0700
Message-ID: <CAJ-VmokGeCLY8pCpL5H0VgznXnB-ob1z_sPaSQUZn0PengSgow@mail.gmail.com> (sfid-20121025_013351_149161_8A377730)
Subject: Re: [ath9k-devel] ath9k_htc and reported mactime
From: Adrian Chadd <adrian@freebsd.org>
To: Thomas Pedersen <thomas@cozybit.com>
Cc: ath9k-devel@lists.ath9k.org,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Bob Copeland <me@bobcopeland.com>
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Sender: linux-wireless-owner@vger.kernel.org

On 24 October 2012 15:08, Thomas Pedersen <thomas@cozybit.com> wrote:

>> Also, we should check to see whether the MAC is paying attention to
>> any beacon frames
>
> How? For mesh mode support we currently just reuse the WDS AP firmware vif
> opmode.
>
>> and updating _its_ timestamp using that beacon frame timer.  That's
>> one of the mesh-and-sta-and-ap-at-the-same-time problems - in
>> STA mode, the TSF gets fudged based on the AP TSF. In other modes this
>> doesn't necessarily hold.
>
> OK, but the TSF for AP shouldn't be automatically updated on other
> beacons, right?

Right but look at those AP macs, there's multiple overlapping TSFs there, right?

* Each MAC AP has an incrementing TSF;
* Multiple APs have different TSF spaces, they're not synchronised at all;
* There's one RX TSF namespace - if the vif is in AP mode then it's
free-running and not synchronising against any other TSF;
* Thus the above makes sense to me.

So far the beacon frames look correct and they're increasing; you're
not obviously synchronising TSF against anything.

Going back to the original question - you fetch TSF after you receive
the packet, and sometimes the TSF in the frame is greater than the TSF
read back by the ath9k TSF get method.
The ath9k_htc tsf read is just 'tsf = ath9k_hw_gettsf64(priv->ah);',
so it's doing direct register reads. That should be immediate, but
it's USB so it may take a while.

So hm, now you've made me open the ath9k_htc firmware source. I hate you.

Let me look.


Adrian