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 >
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