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How to wake-up from RTC-Only mode

Daisuke Maeda
Guru 20425 points

Is the ext_wakeup event required to wake-up from RTC-Only mode?
Can not the internal event be used?

AM335x ARM Cortex-A8 Microprocessors (MPUs) Technical Reference Manual (Rev. F)
http://www.ti.com/lit/ug/spruh73f/spruh73f.pdf
8.1.4.3.6 RTC-Only

Best regards,

Daisuke

 

  • 0
    TI__Guru**** 393215 points
    Hi Daisuke,
     
    Alarm event can also be used, as described in section "20.3.3.7 Power Management" of the AM335X TRM.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 64655 points

    Please read the AM335x Silicon Errata Advisory 1.0.5 for additional infromation related to using the RTC.

    Regards,
    Paul

  • 0 in reply to Biser Gatchev-XID
    Guru 20425 points

    Biser Gatchev-XID said:
    Alarm event can also be used, as described in section "20.3.3.7 Power Management" of the AM335X TRM.
     

     

    Hi Biser,

    Thank you for the reply.

    Can Alarm event be used when only the RTC power supplies are ON and all the remaining power supplies are OFF?
    The RTC power supplies are VDDS_RTC, and CAP_VDD_RTC (if RTC_KALDO_ENn is high).

    In the same case, can the ext_wakeup event be used?

    Best regards,

    Daisuke

     

  • 0 in reply to peaves
    Guru 20425 points

    peaves said:

    Please read the AM335x Silicon Errata Advisory 1.0.5 for additional infromation related to using the RTC.

    Hi Paul,

    Thank you for the reply.

    While the internal 32.768-kHz clock has stopped, can the ext_wakeup event be used?

    Is this errata fixed on AM335x Rev 2.0?

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 393215 points
    Hi Daisuke,
     
    Yes, Alarm event be used when only the RTC power supplies are ON and all the remaining power supplies are OFF, keeping the errata 1.0.5 in mind: "Do not turn off the VDD_CORE power source or source a logic low to the PWRONRSTn input while expecting RTC to keep an accurate time."
     
    For the ext_wakeup event, yes it can be used, again keeping the errata 1.0.5 in mind: "Do not enable the de-bounce circuit on the EXT_WAKEUP input if an external wakeup event needs to be detected while the 32.768-kHz clock is gated."
     
    Also from the TRM: "20.3.3.8 Power Management—System Level (PMIC Mode) The RTC generates pmic_power_en control signal which can be used to control an external PMIC."
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 20425 points

    Hi Biser,

    Biser Gatchev-XID said:
    Yes, Alarm event be used when only the RTC power supplies are ON and all the remaining power supplies are OFF, keeping the errata 1.0.5 in mind: "Do not turn off the VDD_CORE power source or source a logic low to the PWRONRSTn input while expecting RTC to keep an accurate time."
     

     

    I guess that Alarm event is not triggered while the internal 32.768-kHz clock has stopped.
    Therefore, I guess that the conditions below are required for Alarm event.

     - RTC power supplies are ON.

     - VDD_CORE power supply is ON.

     - PWRONRSTn input is High.

     
    Biser Gatchev-XID said:
     
    For the ext_wakeup event, yes it can be used, again keeping the errata 1.0.5 in mind: "Do not enable the de-bounce circuit on the EXT_WAKEUP input if an external wakeup event needs to be detected while the 32.768-kHz clock is gated."
     
     

    I understood that the ext_wakeup event can be used while the internal 32.768-kHz clock has stopped.
    However, in this case the ext_wakeup event is not required because the RTC timer has stopped.

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 393215 points
    Yes Daisuke, that's correct. This is how things stand with Silicon Revision 1.0. I don't have any information yet for the next silicon.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 20425 points

    Hi Biser,

    Thank you for the reply.

    I guess that a power on reset is required to wake-up from RTC-Only mode.
    In other words, it is required that PWRONRSTn input becomes Low.

    I guess that Power-Up Sequencing is required to wake-up from RTC-Only mode.
    If it is correct, it is required that VDD_CORE voltage becomes 0v.

    Therefore, I guess that RTC-only mode is not usable if RTC is required to keep an accurate time.

    I guess that Power-Down Sequencing is required for RTC-Only mode.

    Therefore, I guess that if VDD_CORE power supply is ON, it is required that all other power supplies are ON.

    If above guess are correct, I hope that the errata 1.0.5 is fixed immediately.

    AM335x ARM Cortex-A8 Microprocessors (MPUs) Technical Reference Manual (Rev. F)
    http://www.ti.com/lit/ug/spruh73f/spruh73f.pdf
    8.1.4.3.6 RTC-Only
    26.1.11 Wakeup

    AM335x ARM Cortex-A8 Microprocessors (MPUs) (Rev. D)
    http://www.ti.com/lit/ds/sprs717d/sprs717d.pdf
    4.1.1 Power-Up Sequencing
    4.1.2 Power-Down Sequencing

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 393215 points
    Hi Daisuke,
     
    Well, taking the errata in mind, and if you want to keep accurate time in RTC-only mode, it does look like this mode is practically unusable until hopefully the errata is fixed.
     
    On the other hand, if you don't need accurate time-keeping, then RTC-only mode can be used to conserve power, with the only possibility for wakeup being external input on EXT_WAKEUP (with debounce disabled as per errata).
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 20425 points

    Hi Biser,

    Thank you for the reply.

    Biser Gatchev-XID said:
    On the other hand, if you don't need accurate time-keeping, then RTC-only mode can be used to conserve power, with the only possibility for wakeup being external input on EXT_WAKEUP (with debounce disabled as per errata).
     

    If the VDD_CORE and VDD_MPU power supplies are OFF (0v) or PWRONRSTn input is Low, only the ext_wakeup event with no debounce is usable.
    If all power supplies are ON (active state) and PWRONRSTn input is High, Alarm event and the ext_wakeup event with debounce are usable.

    Our customer requires the lowest power consumption for their application.
    If they do not use RTC, I may recommend that all power supplies which are OFF (0v) are powered up by depending on the external device.

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    TI__Guru**** 393215 points

    Yes Daisuke, that's basically right. If they don't need accurate time-keeping, they still have to init the RTC module, then they can put the device in RTC-only mode, which will cause the RTC to put the power supply IC to sleep via PMIC_PWR_ENABLE signal. Then system can be waked up by external signal on EXT_WAKEUP0, and the RTC module will wake up power supply via PMIC_PWR_ENABLE.

    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 20425 points

    Hi Biser,

    Thank you for the reply.

    If RTC feature is not required, RTC-only mode is not required for the lower power consumption.
    The lowest power consumption is that all power supplies have been powered down to 0v.
    In this case, the external device can initiate Power-Up Sequencing for AM335x.

    Best regards,

    Daisuke

     

  • 0 in reply to Daisuke Maeda
    Prodigy 10 points

    hello,

    do you have some application note to use the rtc with the arm cortex A8 process??

    i'm  looking for an example to configure the rtc register

    thanks

    regards