On Mon, Nov 12, 2012 at 8:32 PM, Bob Copeland <me@xxxxxxxxxxxxxxx> wrote: > On Mon, Nov 12, 2012 at 11:40:15AM -0800, Sam Leffler wrote: >> > I'll do some testing tonight with whatever cards I have around here to >> > see if we can at least get a better idea of which chipsets do what. >> >> >From my experience doing tdma on ath chipsets I know the timestamp is >> a snapshot of the tsf recorded by the dma engine when it writes the >> descriptor on dma completion. This was only legacy frames; don't know >> how things work for aggregate frames. > > On dma completion, so that might be even a bit further beyond > end-of-frame? It's close enough that if you adjust by the air time for the frame you'll get an accurate measure of when the preamble was received at the sta--at least accurate enough for me to synchronize clocks over 100+ km. Details are available if you search and the code has been in freebsd for many years... > > For the record, I just tested this as follows: I set up a mesh > network between an ath5k and an ath9k card (the ath9k driver being > already patched similarly), with the mesh beacon having a few > information elements, and operating in 2.4 GHz band. > > Then I watched toffset adjustments. A more accurate timestamp > means the toffsets between the stations should be closer to each > other. > > Here are some representative numbers: > > ath5k: phy2: Atheros AR2413 chip found (MAC: 0x78, PHY: 0x45) > ------------------------------------------------------------- > Without patch: > updated toffset for 00:80:48:63:a2:f8: 52987952 > updated toffset for 00:03:7f:10:4d:d6: -52989071 > (diff 1119 us) > > With patch: > updated toffset for 00:80:48:63:a2:f8: -92733857 > updated toffset for 00:03:7f:10:4d:d6: 92733496 > (diff 361 us) > > ath5k: phy0: Atheros 5414 chip found (MAC: 0xa3, PHY: 0x61) > ------------------------------------------------------------- > Without patch: > updated toffset for 00:17:f2:43:be:3a: -2557256031 > updated toffset for 00:03:7f:10:4d:d6: 2557254935 > (diff 1096 us) > > With patch: > updated toffset for 00:17:f2:43:be:3a: -2054754842 > updated toffset for 00:03:7f:10:4d:d6: 2054755003 > (diff 161 us) > > Sorry, those are all the ath5k devices I have access to without > digging through some boxes, but in the absence of someone with > old old hardware showing up and saying this is worse for them, > I'd say ship it... > > Thomas, feel free to add my: > > Tested-by: Bob Copeland <me@xxxxxxxxxxxxxxx> > > -- > Bob Copeland %% www.bobcopeland.com -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
