Thanks for your help Janos. If I want the clock error between the root and another mote, would that be the offset? Also, what's is are the timestamps in milliseconds?
David On Mon, Nov 3, 2008 at 8:22 AM, Janos Sallai <[EMAIL PROTECTED]> wrote: > David, > > The local timestamp is the time of reception of a RadioCounToLeds message > according to the motes local clock, whereas the global timestamp is the time > of reception of a RadioCounToLeds message according to the global time in > the network. When a mote is synchronized, they are typically different, so > what you're seeing is correct. > > Regarding the skew being zero: FTSP maintains two local state variables, > skew and offset, which are used to translate local time to global time in > the following way: > > global_time = (1 + skew) * local_time + offset; > > The test app print out skew*1000000, which, per the above definition, should > be pretty close to zero.The 32kHz crystal on the mote has a +-50ppm skew > within the whole operating temperature range. If all the motes are operating > at the same temperature, the skew should be much less than that. I'm seeing > mostly zeros, and -1 here and there. As long as the global times for the > same counter value agree when the network is synchronized, seeing zeros > should not be a problem. > > Please note that, according to the readme file in tests/TestFtsp, a mote > flag is synced if the synced flag is zero.The skew value is only meaningful > when the mote is synced (i.e. the synced flag is zero). > > Janos > > On Mon, Nov 3, 2008 at 9:55 AM, Yi-Tao Wang <[EMAIL PROTECTED]> wrote: >> >> Hi, >> >> I'm having some trouble interpreting the results of the testftsp >> application on tinyos 2.x. The skew value is always 0 even when the >> synched flag is false and global timestamp doesn't equal local >> timestamp. Does anyone know why? >> >> Thanks, >> >> David >> _______________________________________________ >> Tinyos-help mailing list >> [email protected] >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
