Paul Regnier wrote: > Dear Karl, > > I'am working with Mark on some experiments using TDMA and I have some > more doubts. > What happens if the master has no stlot ? In such a case, what should be > the minimum offset > after the Sync frame ?
If the master does not have to transmit any data (no RTcfg?) or uses some time slot later in the frame, you could even set the offset to zero. Of course, no real node will ever be able to hold that schedule, but it will then transmit as soon as possible, right after receiving the Sync frame. > > Using anoter discipline we are developping, we observe the folllowing > fact. Whe the transmission of a > maximum size frame (64b) comes just after the transmission of a mimimum size > frame (1518b), this transmission takes over 250us, When various maximum (You either mixed up the number or the terms... :->) > frame are sent in a row, > the first interarrival time is 230us. Thereafter, all other values are > about 130us, as expected on a 100Mbps > Ethernet medium. Might be some effect of the NIC or its driver. Do you happen to have recorded the traffic on the wire with some sniffer (either on a third node if your switch allows this or on both the sender and the receiver)? If so, what do those packet timestamps tell? > > We believe that the overhead of the first interval is due to the copy of > the message to the buffer > of the Ethernet card (rtl8139, using DMA). Just a kind of pipeline > effect. Do you think this is the case ? Do you send out identical packets? Or why should there only be an impact on the first packet? However, you could additionally analyze your time using some system tracer, either the I-pipe function tracer or LTTng (for the latter, you may have to add some further ad-hoc trace points to RTnet, only RTDM and the Xenomai core are instrumented so far). Jan -- Siemens AG, Corporate Technology, CT SE 26 Corporate Competence Center Embedded Linux ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ RTnet-users mailing list RTnet-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/rtnet-users
