From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Young Subject: Re: TSFT Date: Sat, 17 Nov 2012 00:48:49 -0600 Message-ID: <20121117064848.GO21779@pixotech.com> References: <50A72E17.6070207@superduper.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <50A72E17.6070207-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org" List-Id: radiotap@radiotap.org On Fri, Nov 16, 2012 at 10:26:31PM -0800, Simon Barber wrote: > This is the current definition of TSFT: > > "Value in microseconds of the MAC's 64-bit 802.11 Time > Synchronization Function timer when the first bit of the MPDU > arrived at the MAC. For received frames only." > > My experience with TSFT is with Atheros cards, which record the > timestamp at the end of the frame, not the start. Interesting. Is it consistent across the whole Atheros product line? > Furthermore for DSSS/CCK the definition above is reasonable, but for > OFDM and HT (802.11n) the SIGNAL field (part of the PLCP header, not > part of the MPDU) is part of the first data symbol. It would be much > clearer to change the definition to state that the timestamp is at > the start of this first SIGNAL/data symbol. Any objections to doing > this, or preference to change the reference point to a different > part of the frame? > > In my wireshark patch I've added options to interpret TSFT as the > start of end of the frame. I think we need 1) a methodology for an author to identify their device's reference point so that they can calibrate their driver to the standard and/or 2) a radiotap datum that identifies the reference point in use or 3) something entirely different. Dave -- David Young dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org Urbana, IL (217) 721-9981