3.3.3. Low Power Modes

3.3.3.1. Overview

The following sections describe a high-level description of the different low power modes (LPM) of the device. If your application requires inactive power management, you must determine which low power mode described below satisfies your requirements. Each mode must be evaluated based on power consumption and latency (the time it takes to wakeup to active mode) requirements. Specific values are detailed in the device-specific data sheet. As part of this SDK offering, Texas Instruments has added support for the following low power modes (ordered from lowest power consumption to highest power consumption):

RTC Only Plus DDR
Deep Sleep

3.3.3.2. RTC Only Plus DDR

Note

For this release, the RTC Only + DDR low power mode requires special steps to enter. The steps are documented in System Suspend Mode Workarounds.

RTC Only + DDR mode is the deepest low power mode that allows the system to enter a state of lowest power consumption while still retaining the DDR RAM context.

In order to enter RTC Only + DDR mode, first disable USB0 and USB1 as wakeup sources.

root@am62lxx-evm:~# echo disabled > /sys/devices/platform/bus@f0000/f900000.dwc3-usb/power/wakeup
root@am62lxx-evm:~# echo disabled > /sys/devices/platform/bus@f0000/f910000.dwc3-usb/power/wakeup

Now the SoC can be suspended using the following command.

root@am62lxx-evm:~# echo mem > /sys/power/state
[   67.335138] PM: suspend entry (deep)
[   67.358190] Filesystems sync: 0.019 seconds
[   67.363206] Freezing user space processes
[   67.368991] Freezing user space processes completed (elapsed 0.001 seconds)
[   67.376038] OOM killer disabled.
[   67.379271] Freezing remaining freezable tasks
[   67.384973] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[   67.392398] printk: Suspending console(s) (use no_console_suspend to debug)
NOTICE:  bl1_plat_arch_setup arch setup
NOTICE:  Booting Trusted Firmware
NOTICE:  BL1: v2.12.0(release):11.00.04-7-gaa3963759-dirty
NOTICE:  BL1: Built : 15:56:37, Feb 25 2025
NOTICE:  lpdd4_init <--
NOTICE:  DDR ram size =80000000
NOTICE:  bl1_platform_setup DDR init done
NOTICE:  k3_bl1_handoff sent message to tifs
ERROR:   Wake up src 0x0
ERROR:   Wake up interrupt 0xc
[   67.405953] Disabling non-boot CPUs ...
[   67.408032] psci: CPU1 killed (polled 0 ms)
[   67.408974] Enabling non-boot CPUs ...
[   67.409281] Detected VIPT I-cache on CPU1
[   67.409330] GICv3: CPU1: found redistributor 1 region 0:0x0000000001860000
[   67.409393] CPU1: Booted secondary processor 0x0000000001 [0x410fd034]
[   67.410371] CPU1 is up
[   67.446329] OOM killer enabled.
[   67.449479] Restarting tasks ... done.
[   67.454324] random: crng reseeded on system resumption
[   67.459689] PM: suspend exit

3.3.3.3. DeepSleep

DeepSleep AKA Suspend-to-RAM is a low-power mode that allows the SoC to retain its state in RAM while the processor is turned off. DeepSleep mode is typically used during inactivity when the user requires very low power while waiting for an event that requires processing or higher performance. DeepSleep is a low power mode which still includes DDR in self-refresh, so wakeup events do not require a full cold boot, significantly reducing wakeup latencies. Since the power to Always-On power domains are ON throughout DeepSleep, power to key modules such as GPIO and others is maintained to allow wakeup events to exit out of this mode.

In order to enter DeepSleep,

root@am62lxx-evm:~# echo mem > /sys/power/state
[   88.507502] PM: suspend entry (deep)
[   88.530523] Filesystems sync: 0.019 seconds
[   88.537597] Freezing user space processes
[   88.543218] Freezing user space processes completed (elapsed 0.001 seconds)
[   88.550275] OOM killer disabled.
[   88.553518] Freezing remaining freezable tasks
[   88.559139] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[   88.566570] printk: Suspending console(s) (use no_console_suspend to debug)
ERROR:   Wake up src 0x80
ERROR:   Wake up interrupt 0xc
[   88.591181] Disabling non-boot CPUs ...
[   88.593309] psci: CPU1 killed (polled 0 ms)
[   88.594858] Enabling non-boot CPUs ...
[   88.595327] Detected VIPT I-cache on CPU1
[   88.595379] GICv3: CPU1: found redistributor 1 region 0:0x0000000001860000
[   88.595446] CPU1: Booted secondary processor 0x0000000001 [0x410fd034]
[   88.596420] CPU1 is up
[   88.634778] OOM killer enabled.
[   88.637926] Restarting tasks ... done.
[   88.642801] random: crng reseeded on system resumption
[   88.649913] PM: suspend exit
root@am62lxx-evm:~#

3.3.3.4. Memory Usage

The following table summarizes the usage of memory in different modes of operation of the device.

Domain	Memory	Boot Operation	Normal Operation	Deep Sleep	RTC Only + DDR
WKUP	TIFS SRAM (196 KB)	TIFS load (144 KB) + Sec ROM (20 KB)	TIFS (144 KB)	TIFS (144 KB)	TIFS (144 KB) SEC ROM (20 KB) TIFS_STUB (32 KB)
WKUP	WKUP PSRAM (512 KB)	Pub ROM (64 KB) or (exclusively) PreBL Stack & runtime data (64 KB)		A53 Stub, TF-A Stub (64 KB)	Pub ROM (64 KB)
Main	MAIN MSRAM (96 KB)	PreBL (64 KB) DDR initialization Pub ROM (8 KB) ROM IPC (8 KB)	TIFS IPC (24 KB)	TIFS IPC (24 KB)	PreBL (64 KB) Non-destructive DDR initializtion TIFS IPC + ROM IPC (24 KB) Pub ROM (8 KB)
Main	DDR	Linux TF-A	Linux TF-A	Linux TF-A	Linux TF-A