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CC2640R2F: BLE stack behavior on XTAL oscillator clock source loss

TIDR
Genius 9355 points
Part Number: CC2640R2F
Other Parts Discussed in Thread: CC2640

On the CC2640, if the external clock source at 24MHz fails unexpected is there a facility to switch to HF RC oscillator as the SCLK_HF source. I do see the following CLK_LOSS_EN bits in CTL0 and RESETCTL register. Enabling these bits I presume will cause a reset wherein the software could be programmed to check the reason for reset and switch to using an alternate clock source.


In our software stack, do we have provide an option to do this? Ie are these bits enabled?

If not, do we have reference code showing the correct sequence for these to be handled?

Thanks!!

  • 0
    TI__Genius 10980 points
    Hi,

    Someone is looking into this.

    -Nathan
  • 0
    TI__Guru 56275 points
    Hi,

    The clock loss detection mechanism is for detecting loss of SCLK_LF(RCOSC_LF or 32k xtal). You can find more information in our TRM section 6.7.1.1

    For the 24MHz xtal, every time the device wakes up, it start with using internal high frequency oscillator(RCOSC_HF) as SCLK_HF source and then TI-RTOS will manage the switch by checking if the 24MHz xtal is stable or not. If it's never stable, then the SCLK_HF source will never be switched to 24MHz xtal.

    What's your user case? Is your application going to stay on TX/RX for long time?
  • 0 in reply to Christin Lee
    TI__Genius 9355 points
    Hi
    Yes, I have read section 6.7.1.1 where the LOSS_EN and CLK_LOSS_EN bits are discussed.
    I am aware of the startup condition of the clocks which is discussed as well as the note mentioned in section 6.5.1.1.

    What I'm asking about is the condition where while the chip is operational with the 24MHz clock source, if something happens that causes the clock source to be lost is there provision in the software stack today or automatically via hardware to detect this and switch to RCOSC.

    Thanks!
  • 0 in reply to TIDR
    TI__Guru 56275 points
    No, there is no prevention if the 24MHz xtal stops all of a sudden. That's one of the reason we have the following statement in the datasheet "Probing or otherwise stopping the XTAL while the DC-DC converter is enabled may cause permanent damage to the device."