5.1.7. How to Suspend to RAM (Deep Sleep) on AM62x

AM62x has limited support for Low Power Mode (LPM) in current SDK release. Since not all peripherals drivers are updated to work across suspend/resume cycle,a cut-down version of DT file is provided with limited peripherals and Cores enabled to demonstrate Suspend to RAM (S2R) capability.

Supported Low power mode:

  1. Suspend to RAM (S2R): All power domains are off except for Wakeup Domain that has Wakeup Co-processor (DM R5) running. DDR is in Self Refresh. Switching to LPM demo dts

LPM demo is only possible with cut-down dtb: k3-am625-sk-lpmdemo.dtb. U-Boot needs to be configured to switch to this dtb during kernel Image load and execute

Steps to switch to LPM DT:

  1. Stop boot at U-Boot prompt

  2. Run following cmd

    => run envboot; setenv name_fdt k3-am625-sk-lpmdemo.dtb; run init_mmc; run get_kern_mmc;run get_fdt_mmc;run get_overlay_mmc; booti ${loadaddr} ${rdaddr}:${filesize} ${fdtaddr}
    Alternately, update uEnv.txt to following
    #uenvcmd=run check_for_board; run findfdt
    uenvcmd=run check_for_board; setenv name_fdt k3-am625-sk-lpmdemo.dtb
  3. At Linux prompt, using RTC as wakeup source, test S2R using following cmd

    root@am62xx-evm:~# rtcwake -s 10 -m mem
    rtcwake: wakeup from "mem" using /dev/rtc0 at Fri May 20 09:41:11 2022
    [   42.148655] PM: suspend entry (deep)
    [   42.152391] Filesystems sync: 0.000 seconds
    [   42.166102] Freezing user space processes ... (elapsed 0.001 seconds)    done.
    [   42.175081] OOM killer disabled.
    [   42.178325] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
    [   42.186951] printk: Suspending console(s) (use no_console_suspend to debug)
    [   42.428329] Disabling non-boot CPUs ...
    [   42.826185] OOM killer enabled.
    [   42.829327] Restarting tasks ... done.
    [   42.855525] PM: suspend exit

This puts system to sleep for 10s and then wakes it up via RTC interrupt Limitations

  • Only one A53 core is enabled. Multi-core support is not enabled.
  • Following IPs are enabled in k3-am625-sk-lpmdemo.dts and function across system suspend and resume: UART, I2C, RTC, MMC/SD, MMC/eMMC.

Upcoming releases will add support for additional peripherals and cores.