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 ?
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 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. 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 ? Thanks for your help, Paul > > ---------- Forwarded message ---------- > From: *Karl Reichert* <karl-tra...@gmx.de <mailto:karl-tra...@gmx.de>> > Date: Wed, Dec 17, 2008 at 6:51 AM > Subject: Re: [RTnet-users] TDMA configuration > To: Mark Fernandez <marku...@gmail.com <mailto:marku...@gmail.com>>, > rtnet-users@lists.sourceforge.net > <mailto:rtnet-users@lists.sourceforge.net> > > > Hi Mark, > > > Hi. I'm trying to do some experiments using the tdma.conf file. I wonder > > what is the minimum value to reserve for the sync frame in the cycle > > begining? Is it 200 us? > If the master (the one that is sending the sync frames) is meant to be > the first station transmitting a data frame after the sync frame in > each cycle, you can set the offset to 0 in tdma.conf. Because both > frames, sync and data are send by the same station (the master), RTnet > will take care, that there will be no collision. As a sideeffect, this > will minimize the gap between sync and data frame. > > > And what is the minimum offset to a station that > > just transmit messages of 64Bytes ? Can I set 30 us? > Depends on how fast is your network and especially how low is your > clock jitter. I would give it a try, if you encounter problems with > this setup, increase the offset. > > Best regards > Karl > -- > von Karl Reichert > > ------------------------------------------------------------------------------ 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
