Hi Eric, 0.238us is just 1/4uis. Note the DCO of TelosB runs at 4MiHz, a DCO tick would be 1/(4*1024*1024)=0.238us. This sub-microsecond level of precision is desirable for my application, not 1us level. I have checked the src code of tos/chips/msp430/timer. The SMLK of the MCU is DCO/4=1MiHz, It is a little bit confusing here, i don't know why the default frequency divider of SMLK is set to 4. Is it because of the unstable nature of the DCO if it runs at high frequency( 4MiHz or higher)? If i want a faster timer, can I directly set the frequency divider to 1 (by setting the register BCSCTL2=0)? In this way, timerA of MSP430 which is sourced by SMLK will run exactly at 4MiHz. Reading the TAR register directly sounds good, i shall try it.
Thank you Eric. 2014-03-27 14:41 GMT+08:00 Eric Decker <[email protected]>: > > > > On Tue, Mar 25, 2014 at 7:58 AM, Dingming Wu <[email protected]> wrote: > >> Hello everyone, >> >> I am running an application requires time information with very high >> precision. I know the MCU of TelosB has an internal DCO runs at a frequency >> of 4MHz, which means a DCO tick or a no operation instruction of the MCU >> is 0.238us. This time precision is high enough for my application. >> > > Not sure how you got a DCO tick is 0.238 uS. > > TinyOS on the telosb uses binary time and the DCO is actually running at > 4 MiHz = 1024x1024x1024 Hz > > What I do is use the underlying registers from the msp430f1611, TAR. > > I've added a TinyOS interface to these low level registers but that is in > the tp-freeforall repository. > > But I would recommend you fudge it and just use the register directly. It > is programmed to tick with 1uis (binary us) resolution. > > > >> But the existing timers on TelosB can count at a precision of at most >> microsecond level. To obtain even higher time resolution, e.g. >> sub-microsecond, is it possible to measure the number of DCO ticks in >> TinyOS? For example, can i measure the # of ticks between two instants of >> transitions of the SFD pin? >> >> >> -- >> Regards, >> 鼎名 >> >> _______________________________________________ >> Tinyos-help mailing list >> [email protected] >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >> > > > > -- > Eric B. Decker > Senior (over 50 :-) Researcher > > -- Regards, 鼎名
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