Re: [Madwifi-devel] Fwd: TX tstamp value and ATH_TX_INT
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From: Michael T. <mik...@ap...> - 2007-06-15 03:32:57
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#ffffff" text="#000000"> Just to clarify:<br> <br> When we have extended the t_stamp with the 64-bit TSF, it's then microseconds, correct? I have been working with the extended t_stamp (TSF) value primarily and looking at relative timing values across received events (i.e. radar).<br> <br> Thanks,<br> <br> Mike<br> <br> Steve Glass wrote: <blockquote cite="mid:2f1...@ma..." type="cite"><span class="gmail_quote"></span>Hi<br> <br> The TX timestamps can be a surprise - I've lots of captures where time "goes backwards" because the TX timestamp pre-dates many of the RX frames that are captured before it. That's purely an implementation artefact and I've written awk scripts and such to correct this but I wouldn't trust the timestamps for any serious experimental purposes. <br> <br> I do have a prism 11b card - which does have 1us resolution - and a cursory inspection convinced me the timestamp is for when the frame is finally successfully sent (it may even be for the ACK receipt). YMMV as I've yet to confirm this with any degree of rigor and my recollection maybe faulty. I'll retry this at the weekend and compare captures to see exactly what's happening. <br> <br> Steve <div><span class="e" id="q_1132c894c5943f7e_1"><br> <br> <div><span class="gmail_quote">On 6/15/07, <b class="gmail_sendername">Scott Raynel</b> <<a moz-do-not-send="true" href="mailto:sco...@gm..." target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> sco...@gm...</a>> wrote:</span> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi,<br> <br> Just being pedantic, but...<br> <br> On 15/06/2007, at 3:50 AM, Michael Taylor wrote:<br> <br> ><br> >> Does the 'ts_tstamp' value represent the duration of time taken to<br> >> send the<br> >> frame over the medium or does it measure some other time duration <br> >> like time in<br> >> queue?<br> >><br> > It's not a duration, it's a time stamp. It represents the instant the<br> > frame was received with microsecond resolution.<br> <br> This is correct for the RX path, but on the TX path it represents the <br> time the frame was transmitted by the hardware, and for various<br> reasons has an accuracy of TU's, not microseconds (hence the shift<br> left by 10). I have talked to Sam about this before, and he couldn't<br> tell me exactly *when* the frame is stamped on it's way out - for<br> example, is the timestamp for the first, second, last retransmit of a<br> frame? We don't know.<br> <br> Have a good one,<br> <br> --<br> Scott Raynel <br> WAND Network Research Group<br> Department of Computer Science<br> University of Waikato<br> New Zealand<br> <br> <br> <br> <br> -------------------------------------------------------------------------<br> This SF.net email is sponsored by DB2 Express <br> Download DB2 Express C - the FREE version of DB2 express and take<br> control of your XML. No limits. Just data. Click to get it now.<br> <a moz-do-not-send="true" href="http://sourceforge.net/powerbar/db2/" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://sourceforge.net/powerbar/db2/ </a><br> _______________________________________________<br> Madwifi-devel mailing list<br> <a moz-do-not-send="true" href="mailto:Mad...@li..." target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">Mad...@li... </a><br> <a moz-do-not-send="true" href="https://lists.sourceforge.net/lists/listinfo/madwifi-devel" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">https://lists.sourceforge.net/lists/listinfo/madwifi-devel</a><br> </blockquote> </div> <br> <br clear="all"> <br> </span></div> <span class="sg">-- <br> The day Microsoft sells something that doesn't suck is the day they start selling vacuum cleaners. </span><br clear="all"> <br> -- <br> The day Microsoft sells something that doesn't suck is the day they start selling vacuum cleaners. <pre wrap=""> <hr size="4" width="90%"> ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. <a class="moz-txt-link-freetext" href="http://sourceforge.net/powerbar/db2/">http://sourceforge.net/powerbar/db2/</a></pre> <pre wrap=""> <hr size="4" width="90%"> _______________________________________________ Madwifi-devel mailing list <a class="moz-txt-link-abbreviated" href="mailto:Mad...@li...">Mad...@li...</a> <a class="moz-txt-link-freetext" href="https://lists.sourceforge.net/lists/listinfo/madwifi-devel">https://lists.sourceforge.net/lists/listinfo/madwifi-devel</a> </pre> </blockquote> </body> </html> |