Hi, I would think so. If you use just the DCO, without any calibration, the error will be very high. >From datasheet numbers for MSP430F1611:
Temperature sensitivity is about 0.38% / degC (from a nominal at 25 degC) at 3V. Voltage sensitivity is about 5% / V. Since the frequency vs temperature and frequency vs voltage characteristics are highly non-linear, it is hard to come up with a good relationship that will capture both effects together, but you get an idea of how 'bad' a DCO is (I must emphasize that this is without calibration). If you calibrate a DCO well enough, it can give you a pretty stable clock. To my understanding TinyOS does perform calibration at boot up. See http://mail.millennium.berkeley.edu/pipermail/tinyos-help/2007-September/027998.html Zainul. On Sat, Oct 18, 2008 at 2:27 PM, Somnath Mitra <[EMAIL PROTECTED]> wrote: > Hello Zainul, > > Thanks for your reply. You said that the freq error (worst case) for the 32 > Khz crystal is 40 ppm. What if we use the internal DCO ? will our internal > freq error go up ? > > Thanks, > > Somnath > > On Sat, Oct 18, 2008 at 3:35 PM, Zainul M Charbiwala <[EMAIL PROTECTED]> > wrote: >> >> Hi Somnath, >> >> The main clock on the Telos motes runs on an internal DCO which has a >> lot of frequency error (could be on the order of 10%), unless the >> error is corrected through periodic recalibration with the crystal. >> >> I believe the timers are run off the 32KHz crystal in TinyOS, which >> would lead to a worst case of 40ppm freq error. >> >> The clock drift is essentially (in sec), drift = >> (time_since_last_sync)*(freq_error_in_ppm)/1e6. >> >> This means that if you don't resync periodically, your clock drift >> could be unbounded. >> Hope this answers your question. >> >> Zainul. >> >> On Sat, Oct 18, 2008 at 1:17 PM, Somnath Mitra <[EMAIL PROTECTED]> wrote: >> > Hello , >> > >> > People who have worked on time synchronization, can anyone please tell >> > me >> > that - >> > >> > Can we say that there is a maximum upper bound on the amount of drift of >> > the >> > clocks of Telos like platforms ? >> > >> > Thanks, >> > >> > Somnath Mitra >> > >> > _______________________________________________ >> > 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
