Hi, *>The DCO takes something like 3.5uS to come out of sleep and when syncronized to the 32KiHz Xtal is pretty stable because it is automatically (via h/w) being tweaked to be pretty stable.* Do you have any typical number on the stability of DCO's frequency? 32KiHz Xtal usually drifts up to 40 ppm.
Another follow up question, for a Xtal, given its frequency drift, it is the maximum. In reality, the frequency varies over time, even it's bounded. How fast does the frequency change, typically? (For simplicity, we can assume other factors do not change, e.g., temperature.) Even time sync protocols such as *ftsp* estimate local clock skew via linear regression, the skew seems time-varying (as Figure 5<http://www.math.u-szeged.hu/tagok/mmaroti/okt/2010t/ftsp.pdf>shows). Thus, it necessitates continuous re-sync. The same question applies for DCO. Thank you all for your hints. On Sun, May 12, 2013 at 4:56 PM, Eric Decker <[email protected]> wrote: > > The biggest problem with a crystal is it is a power hog. > > Also takes a long time to stabilize when coming out of sleep. And if you > are trying for low power, you want to sleep the cpu most of the time. > > I think I measured an 16 MHz Xtal as taking 5 ms to stabilize coming out > of sleep. I don't remember the details though. But it was enough for us > to reject it in our design. > > The DCO takes something like 3.5uS to come out of sleep and when > syncronized to the 32KiHz Xtal is pretty stable because it is automatically > (via h/w) being tweaked to be pretty stable. > > All the above is written assuming a 5438a > > > On Sun, May 12, 2013 at 1:31 PM, Xiaohui Liu <[email protected]> wrote: > >> Hi, >> >> Thanks for the reply. >> >> If quartz crystal oscillator is used, it mostly does not drift more than >> 40 ppm. What about DCO's frequency drift? >> >> Cheers, >> -Xiaohui >> >> >> >> On Fri, May 10, 2013 at 8:22 PM, Jeonghoon Kang <[email protected]>wrote: >> >>> Most answers are on the the datasheet. >>> Good luck ! >>> >>> >>> http://www.google.co.kr/#newwindow=1&sclient=psy-ab&q=dco+msp430+datasheet&oq=dco+msp430+datasheet&gs_l=hp.3...5186.6707.1.6864.10.10.0.0.0.0.138.930.6j3.9.0...0.0...1c.1.12.psy-ab.ITpRwb2Ld9I&pbx=1&bav=on.2,or.r_qf.&bvm=bv.46340616,d.aGc&fp=c76d164efb6c1041&biw=1177&bih=775 >>> >>> >>> >>> >>> 2013/5/11 Xiaohui Liu <[email protected]> >>> >>>> Hi everyone, >>>> >>>> One of the clock sources in TelosB is digitally-controlled oscillator >>>> (DCO). How does it work? How does it compare to RC oscillator and MHz >>>> quartz crystal oscillator, in terms of expense, accuracy, stability and >>>> etc.? >>>> >>>> Thanks. >>>> >>>> -- >>>> -Xiaohui Liu >>>> TelosB >>>> TinyOS 2.1.2 >>>> www.cs.wayne.edu/xliu/ >>>> >>>> _______________________________________________ >>>> Tinyos-help mailing list >>>> [email protected] >>>> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >>>> >>> >>> >> >> >> -- >> -Xiaohui Liu >> TelosB >> TinyOS 2.1.2 >> www.cs.wayne.edu/xliu/ >> >> _______________________________________________ >> Tinyos-help mailing list >> [email protected] >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >> > > > > -- > Eric B. Decker > Senior (over 50 :-) Researcher > > -- -Xiaohui Liu TelosB TinyOS 2.1.2 www.cs.wayne.edu/xliu/
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