4.7. Android Low Power Support

This application note contains steps to enable low power support in BSP.

Supported low power mode:

1. Suspend to RAM (S2R): All power domains are off except for wake-up domain that has wake-up co-processor (DM R5) running. DDR is in self refresh.

Note

OP-TEE OS debug logs are disabled by default. However, if you enable them for debugging purposes (CFG_TEE_CORE_LOG_LEVEL > 0), the suspend/resume functionality will not work properly. Make sure to disable OP-TEE OS logs when testing low power modes.

4.7.1. Enable Suspend/Resume support

1. At Android prompt, using RTC as wake-up source, test S2R using following command:

   console:/ $ su
   console:/ # rtcwake -s 10 -m mem
   wakeup using "mem" from /dev/rtc0 at Mon Feb 27 20:47:02 2023
   [  171.729145] PM: suspend entry (deep)
   [  171.737476] Filesystems sync: 0.004 seconds
   [  171.742214] Freezing user space processes ... (elapsed 0.004 seconds) done.
   [  171.754087] OOM killer disabled.
   [  171.757326] Freezing remaining freezable tasks ... (elapsed 0.003 seconds) done.
   [  171.784455] android_work: sent uevent USB_STATE=DISCONNECTED
   [  171.961454] Disabling non-boot CPUs ...
   [  171.970763] psci: CPU1 killed (polled 4 ms)
   [  171.993689] psci: CPU2 killed (polled 0 ms)
   [  172.014894] psci: CPU3 killed (polled 4 ms)
   [  200.067533] am65-cpsw-nuss 8000000.ethernet eth0: PHY [8000f00.mdio:00] driver [TI DP83867] (irq=POLL)
   [  200.076971] am65-cpsw-nuss 8000000.ethernet eth0: configuring for phy/rgmii-rxid link mode
   [  200.103015] am65-cpsw-nuss 8000000.ethernet eth1: PHY [8000f00.mdio:01] driver [TI DP83867] (irq=POLL)
   [  200.112422] am65-cpsw-nuss 8000000.ethernet eth1: configuring for phy/rgmii-rxid link mode
   [  200.454835] OOM killer enabled.
   [  200.457993] Restarting tasks ...
   [  200.505711] android_work: sent uevent USB_STATE=CONNECTED
   [  200.527147] dwc3 31000000.usb: request 0000000000000000 was not queued to ep0out
   [  200.687139] done.
   [  200.689205] Resume caused by IRQ 15, 2b1f0000.rtc
   [  200.701243] read descriptors
   [  200.705646] read strings
   [  200.711041] android_work: sent uevent USB_STATE=DISCONNECTED
   [  200.734919] PM: suspend exit
   console:/ # [  201.555258] android_work: sent uevent USB_STATE=CONNECTED
   [  201.595880] android_work: sent uevent USB_STATE=CONFIGURED
   console:/ $
   

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