RTOS/CC1310: Is it possible to run the timer or clock from the 24 MHz xtal?

Part Number: CC1310

Tool/software: TI-RTOS

I'm trying to time-synchronise two wireless devices. To do this I'm transmitting the RAT timer value, which uses the 24MHz clock, and using as the base to syncrhonise the base time. The next transmission is set up,  timed by a clock, which by default uses the 32KHz source meaning the possible max drift of the clock is compounded by having to account for two crystal inaccuracies (10ppm * 2 xtals * 2 devices).

Is there any way to set a specific clock or timer to utilise the 24MHz clock so that I do not have this problem?

Would this timer be able to continue to tick while in standby mode between communications? 

5 Replies

  • Can anyone help me out with some info here?

    Cheers,
    Craig
  • In reply to Craig E:

    Hi Craig,

    In CCFG you can select the 24 MHz crystal oscillator as source for the RTC. This will also force the 24 MHz oscillator to stay on in Standby. Note that current consumption, also in Standby, will increase by approximately 40 uA in this mode.

    Regards,
    Fredrik
  • In reply to Fredrik K:

    Thanks Fredrik, good to know!

    > Note that current consumption, also in Standby, will increase by approximately 40 uA in this mode.

    That is quite unfortunate since the point of doing this was to reduce the size of the RX sync window to save power!

    How is it that the RAT timer can keep time in standby mode when it's based off the 24MHz clock? Or am I misguided in that assumption?
  • In reply to Craig E:

    Hi Craig,

    The RAT timer is not able to run in Standby, it only runs when the RF Core is enabled.

    In Standby, unless you force the 24 MHz as I mentioned above, the only running clock is the RTC which is based on either the 32k RC oscillator or the 32k crystal oscillator.
  • In reply to Craig E:

    > How is it that the RAT timer can keep time in standby mode when it's based off the 24MHz clock? Or am I misguided in that assumption?

    It doesn't.

    TI-RTOS's RF driver finds the correlation between RAT timer and RTC before sleep, then re-inits the RAT to an appropriate value during wake.

    There's a little drift in this process, but it's close enough to keep multiple ultra-low-power nodes in sync, which my application also involves.