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CC3200 Request Clarification on Hibernate OCR/RTC Register Usage within Power Management Framework

Craig Carson
Intellectual 780 points
Other Parts Discussed in Thread: CC3200

My understanding is there are 2 registers which are retained across a hibernate power cycle.  The two registers are located at the following memory addresses:

Base = 0x4402F800

Reg2 = Base + 0x420         Reg3 = Base + 0x424

In the technical documentation it indicates these registers are available for the application to use for OCR (On Chip Retention).  Additionally in the documentation it states these registers are used by the RTC and if the RTC is being used they are no longer available for application use.

It appears the only use the RTC has for Reg2 & Reg3 is for storing calendar time adjustment value.  Is this correct?

I assume the values in Reg2 & Reg3 are NOT accessed by the MCU while the chip is in hibernation.  Is this correct?

If both my assumptions above are correct is it save to say the OCR registers can still be used by the application alongside the RTC as long as no adjustment to the RTC is required by the application?  I do realize some workaround would be required if this is true (such as immediately reading register values on wakeup followed by a call to cc_rtc_init immediately after).  I just want to check that even if this will work today I'm not setting myself up for a problem down the road.

  • 0
    TI__Expert 5660 points
    Hi Craig,

    Please find below info regarding how the RTC functionality is realized in CC3200. Note that CC3200 does not have a true RTC capability. The below description should answer your queries
    // The implementation to support RTC has been kept very simple. A set of
    // HIB Memory Registers in conjunction with Slow Clock Counter are used
    // to render RTC information to users. Core principle of design involves
    // two steps (a) establish an association between user provided wall-clock
    // and slow clock counter. (b) store reference value of this associattion
    // in HIB Registers. This reference value and SCC value are then combined
    // to create real-world calendar time.
    //
    // Across HIB cycles, value stored in HIB Registers is retained and slow
    // clock counter continues to tick, thereby, this arragement is relevant
    // and valid as long as device has a (tickle) battery power.

    Please find below responses to your specific queries
    It appears the only use the RTC has for Reg2 & Reg3 is for storing calendar time adjustment value. Is this correct?
    [Siddaram] No These registers hold the RTC reference value. So if these are used for some other purpose, All you will be left with is a slow clock counter but the reference value is lost. You need both to realize the RTC functionality.

    I assume the values in Reg2 & Reg3 are NOT accessed by the MCU while the chip is in hibernation. Is this correct?
    [Siddaram]As mentioned above these are used to store the reference value.

    So if you decide to use Reg2 and Reg3 for other purposes then PM framework will work only on relative time and not absolute time. To work with PM framework using absolute time these two registers have to be reserved for usage by RTC


    Thanks and Regards,
    Siddaram
  • 0 in reply to Siddaram Mathapathi
    TI__Expert 5660 points
    Hi Craig,

    Did your queries got answered. If yes please press the "Verify Answer" button to close this thread.

    Thanks and Regards,
    Siddaram