> > Hello, > > > > I read the paper "RTnet – A Flexible Hard Real-Time Networking > Framework" at http://www.rts.uni-hannover.de/rtnet/download/RTnet-ETFA05.pdf > and I > have a question concerning chapter 3.2, formula 3. > > > > T_slot = T_sched + t_slot - t_offset > > > > As far as I understand this formula, the slaves calculate their own > starting point T_slot from T_sched (the planned transmission time of master), > t_slot (slot duration?) and t_offset (offset between master and slave > clock). To my mind, this doesn't makes any sence. Maybe I misunderstand one of > the variables, but let me give a small example: > > > > T_sched = 15 (absolute time point) > > t_slot = 10 (duration) > > t_offset = 20 > > > > Then, slave's starting point would be 15+10-20=5 > > But how is it possible, if the master is the first one sending? I don't > understand this formula. > > Oops, you stumbled over an impreciseness of the variables in that paper. > They must read T_sched,master and T_slot,slave, i.e. the first one is > related to the master view of time while the second one was transformed > to the slave time base. > > Jan > But still, this doesn't makes sense to me. As I understand the paper, formula 2 and 3 should fix potential scheduling jitters (the time difference between scheduled and "real" sending time on the master). But how can this be fixed, if the formula deals with the T_master_sched and not the T_master_real (=T_master_xmit)?
Let me give an example: at the same point of time (the moment the master sends sth), master clock=10, slave clock=30 the master jitter may be 2, which means that T_master_sched=10 and T_master_xmit=12 t_travel may be 3 t_slot (Slot-Length) may be 5 t_offset=12+3-35=-30 T_slave_slot=10+5+30=45 To my mind, this is the _scheduled_ slave slot time (the time, the slave would send, if there wouldn't be any master's jitter), seen from slave's point of view. But to respect the master's jitter, the formula to calculate the _real_ slave slot time should be: T_slave_slot = T_master_xmit + t_slot - t_offset which would result in: T_slave_slot=12+5+30=47 Do I understand sth wrong or would you agree with that? Thanks Karl -- von Karl Reichert "Feel free" - 10 GB Mailbox, 100 FreeSMS/Monat ... Jetzt GMX TopMail testen: http://www.gmx.net/de/go/topmail ------------------------------------------------------------------------- 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. http://sourceforge.net/powerbar/db2/ _______________________________________________ RTnet-users mailing list RTnet-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/rtnet-users
