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AM3352: Low power mode support

Sung-IL
Mastermind 31510 points

Part Number: AM3352

Dear Champs,

My customer want to implemented low-power system - Power-efficient display-based application' described in 'Power optimization techniques for energy-efficient systems(spry241.pdf)', and requested how it can be implemented.

I'm curious if low-power mode can be supported in AM3352 now. Could you please check if low-power mode described in spry241.pdf document is still supported in AM3352?

* low-power mode can be supported in AM3352 device?

    - If so, what is the CPU freq at this low-power mode?

    - this low-power mode can be supported in Linux PSDK?

    - could you please let me know which SDK SW can support this low power mode?

Thanks and Best Regards,

SI.

  • 0
    TI__Guru**** 393215 points
    Hi,

    Yes, this document is valid. Please see processors.wiki.ti.com/.../Linux_Core_Power_Management_User's_Guide_(v4.1) for more information on power management in the Processor SDK - Linux.
  • 0 in reply to Biser Gatchev-XID
    TI__Mastermind 31510 points
    Thanks Biser,

    But, I could not find any description for 25Mhz CPU clock in any documents, and I could not find any OPP mode for 25Mhz CPU clock operation. I'm still wondering if CPU can be run at 25Mhz CPU clock as described in above state machine.

    When I checked the document of processors.wiki.ti.com/.../Linux_Core_Power_Management_User's_Guide_(v4.1) , I only find 'powersave' mode, but I don't know if CPU can be run at 25Mhz CPU clock in this powersave mode.

    powersave: This governor statically sets the OPP of the MPU to the lowest possible frequency.


    But, I could not find what is the lowest possible frequency in AM335x, but found CPU clock of lowest OPP is 275Mhz in the datasheet.

    Could you please make me more clear on this?
    If it is possible to run CPU(MPU) at 26Mhz, could you please let me know the procedure how they can achieve this lowest CPU clock?
    is it OK to use powersave mode described in processors.wiki.ti.com/.../Linux_Core_Power_Management_User's_Guide_(v4.1) ?


    Thanks and Best Regards,
    SI.
  • 0 in reply to Sung-IL
    TI__Guru**** 170625 points

    Sung-IL said:
    But, I could not find any description for 25Mhz CPU clock in any documents, and I could not find any OPP mode for 25Mhz CPU clock operation. I'm still wondering if CPU can be run at 25Mhz CPU clock as described in above state machine.

    In this spry241.pdf we have:

    The AM335x processors support five different operating points: OPP50, OPP100, OPP120, Turbo and Nitro. With a wide frequency range of 10MHz to 1GHz, it provides flexible configuration.

    In addition to turning off the display, the processor frequency can be reduced to as low as 10MHz.

    Yes, AM335x A8 CPU frequency can be run at 10MHz, 24MHz, 25MHz and 26MHz. At OPP50 we have MAX value of 300MHz and MIN value of 10MHz. See AM335x datasheet, Table 5-7, note (1) - Frequencies in this table indicate maximum performance for a given OPP condition

    Note that Cortex-A8 at OPP50 for silicon revision 1.0 is not supported, see silicon errata for more details.

    Sung-IL said:
    If it is possible to run CPU(MPU) at 26Mhz, could you please let me know the procedure how they can achieve this lowest CPU clock?

    Yes, you can. You should change the MPU DPLL settings.

    Sung-IL said:
    is it OK to use powersave mode described in processors.wiki.ti.com/.../Linux_Core_Power_Management_User's_Guide_(v4.1) ?

    Note that "Low Power" mode from the spry241.pdf is actually active mode (PLL is locked, DDR is active). The "Suspend" mode is the one described in TI wiki

    Regards,
    Pavel

     

  • 0 in reply to Pavel Botev
    TI__Guru**** 170625 points
    See also the below e2e thread:

    e2e.ti.com/.../186825

    Regards,
    Pavel
  • 0 in reply to Sung-IL
    TI__Genius 13515 points

    Hi Sung IL,

    Can you explain what MPU activity will be occurring during the low power mode?  Will the MPU be idle, or will low-priority processing be happening?

    By default, in Linux Processor SDK, during periods the MPU is idle, AM335x automatically goes into MPU WFI + MPU PLL bypass.  The MPU is consuming minimal power in this mode.

    If you need to define a new minimum frequency for background tasks in the low power mode, you can do so as Pavel and Biser have mentioned.  Please note beginning with Processor SDK 3.0 (Linux kernel version 4.4+), the OPP table is now in the device tree (cpu0_opp_table in am33xx.dtsi).

    Regards,
    Mike