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feat(linux): AM62Lx: Add documentation for RTC Only mode
Add documentation on how to enter RTC Only low power mode on AM62L EVM. This includes all the prerequisites and alternatives to enter this mode. Signed-off-by: Akashdeep Kaur <a-kaur@ti.com>
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‎source/images/am62l_lpm_j14.png‎

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‎source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst‎

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@@ -15,9 +15,71 @@ values are detailed in the device-specific data sheet. As part of this SDK offer
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Texas Instruments has added support for the following low power modes (ordered from lowest power consumption
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to highest power consumption):
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#. RTC Only
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#. RTC Only Plus DDR
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#. Deep Sleep
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RTC Only
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********
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RTC Only mode is the deepest low power mode that allows the system to enter a complete poweroff state
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with ultra-low power consumption while maintaining system time and wakeup capability.
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Unlike other low power modes, RTC Only powers off all domains except the RTC, which remains active
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to keep track of system time and provide wakeup via RTC alarm or RTC I/O event.
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.. note::
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The system loses nearly all its state as DDR is also turned-off.
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RTC Only is comparable with a Linux poweroff state with system timer ON.
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.. important::
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Jumper J14 position on the EVM determines which low power mode is entered. For RTC Only mode,
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connect jumper J14 to the position marked as "RTC ONLY MODE".
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.. image:: /images/am62l_lpm_j14.png
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The reference implementation in this SDK implements RTC Only as a poweroff state.
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When the system powers off, the RTC driver programs the RTC hardware for poweroff mode.
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The final sequence to power off the system is executed by TF-A firmware, which pulls the PMIC_EN
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signal low to turn off all the supply rails powered by the PMIC.
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On AM62L platforms, if the ``system-power-controller`` device tree property is not set on the PMIC node,
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the PMIC will not register a poweroff handler. In this configuration, TF-A firmware handles the
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poweroff sequence and the system enters RTC Only mode. This allows the system to maintain accurate
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system time and provide wakeup capability via RTC alarm or external button press while consuming
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minimal power.
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RTC Only mode supports two wakeup sources: RTC timer alarm and RTC I/O pins.
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Use the following command to enter RTC Only mode with a timer alarm for wakeup:
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.. code-block:: console
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root@<machine>:~# rtcwake -s <time> -m off
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Use the following command to enter RTC Only mode with RTC I/O (button press) for wakeup:
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.. code-block:: console
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root@<machine>:~# poweroff
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At this point, the Linux kernel will go through its poweroff process and
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the console output will stop at the following lines:
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.. code-block:: dmesg
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[ 51.698039] systemd-shutdown[1]: Powering off.
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[ 51.769478] reboot: Power down
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The system has entered RTC Only mode and can be woken up by activity on an RTC I/O pin
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programmed for wakeup. If an alarm was set, the system will automatically wake up
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when the alarm triggers.
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During resume from RTC Only mode, the system goes through a normal Linux boot process. The RTC driver
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detects that the RTC is already programmed and skips the full initialization, performing only minimal
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cleanup to preserve the system time.
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RTC Only Plus DDR
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*****************
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‎source/linux/Foundational_Components/Power_Management/pm_overview.rst‎

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The static power management features on |__PART_FAMILY_DEVICE_NAMES__| are:
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#. RTC Only
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#. RTC Only Plus DDR
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#. Deep Sleep

‎source/linux/Foundational_Components/Power_Management/pm_wakeup_sources.rst‎

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.. ifconfig:: CONFIG_part_variant in ('AM62LX')
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+------------------------------------------------+------------+----------------+
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| Wakeup Source | Deep Sleep | RTC Only + DDR |
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+================================================+============+================+
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| Real-Time Clock (RTC) | Yes | Yes |
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+------------------------------------------------+------------+----------------+
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| WKUP GPIO | Yes | No |
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+------------------------------------------------+------------+----------------+
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| Main I/O Daisy Chain (Main GPIO and Main UART) | Yes | No |
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+------------------------------------------------+------------+----------------+
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| WKUP UART | Yes | No |
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+------------------------------------------------+------------+----------------+
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| USB Wakeup | Yes | No |
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+------------------------------------------------+------------+----------------+
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| RTC Ext Pin | Yes | Yes |
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+------------------------------------------------+------------+----------------+
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+------------------------------------------------+------------+----------------+----------+
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| Wakeup Source | Deep Sleep | RTC Only + DDR | RTC Only |
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+================================================+============+================+==========+
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| Real-Time Clock (RTC) | Yes | Yes | Yes |
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+------------------------------------------------+------------+----------------+----------+
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| WKUP GPIO | Yes | No | No |
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+------------------------------------------------+------------+----------------+----------+
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| Main I/O Daisy Chain (Main GPIO and Main UART) | Yes | No | No |
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+------------------------------------------------+------------+----------------+----------+
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| WKUP UART | Yes | No | No |
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+------------------------------------------------+------------+----------------+----------+
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| USB Wakeup | Yes | No | No |
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+------------------------------------------------+------------+----------------+----------+
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| RTC Ext Pin | Yes | Yes | Yes |
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+------------------------------------------------+------------+----------------+----------+
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*********************
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Real-Time Clock (RTC)

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