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Version: Torizon OS 7.x.y

How to Suspend/Resume on Torizon OS

Introduction​

This case-oriented article delves into the process of suspending and resuming a SoM running on Torizon OS. By using a containerized environment, you can achieve low-power modes without root permissions, streamlining the integration of power management strategies into your applications.

Reboot and Suspend/Resume​

Altering the power state usually requires root permissions. Since running containers with root (privileged) permissions isn't in best practices, these tasks can be performed without root permissions inside a container. The key to success is using a bind mount for the required files - and it can be applied in many scenarios, not only this one.

From a security perspective, bind mounting /proc/sysrq-trigger, which allows performing some low-level commands, or /var/run/dbus, which provides access to system services, may potentially pose a vulnerability, even though this is probably more secure than a regular non-containerized embedded use case.

Reboot via D-Bus is a more proper way to do it, since it will gently ask all daemons and containers to stop before reboot, while sysrq will not do that. Learn more about sysrq-trigger options in the Linux kernel documentation page Linux Magic System Request Key Hacks to decide if this is acceptable to bind mount in your case.

Prerequisites​

Reboot​

The below example reboots the device by writing to /proc/sysrq-trigger:

# docker run -it --rm -v /proc/sysrq-trigger:/procw/sysrq-trigger torizon/debian:3-bookworm
## echo "b" > /procw/sysrq-trigger

Or reboot with using D-Bus:

# docker run -it --rm -v /var/run/dbus:/var/run/dbus torizon/debian:3-bookworm
## apt update &&  apt-get install -y dbus
## dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1 "org.freedesktop.login1.Manager.Reboot" boolean:true

It is also possible to use a D-Bus library for your preferred language. If you use Python, you can use our D-Bus Python sample as a starting point.

Suspend and Wake-Up​

You can put the system into supported low-power modes without root permissions inside a container. For a general list of supported power modes by our BSP, see the article Suspend/Resume (Linux).

The below examples suspends/resumes the device by writing to the various files:

Suspend and wakeup using RTC​

# docker run -it --rm -v /sys/class/rtc/rtc1/wakealarm:/sys/class/rtc/rtc1/wakealarm -v /sys/power/state:/sys/power/state torizon/debian:3-bookworm
## echo +5 > /sys/class/rtc/rtc1/wakealarm; echo mem > /sys/power/state

Suspend and wakeup over UART​

# docker run -it --rm -v /sys/class/tty/ttymxc0/power/wakeup:/sys/class/tty/ttymxc0/power/wakeup -v /sys/power/state:/sys/power/state torizon/debian:3-bookworm
## echo enabled > /sys/class/tty/ttymxc0/power/wakeup
## echo mem > /sys/power/state
Press any button to wakeup from suspend...

Some SoMs require to use a different UART (e.g. ttyLP3 on Colibri iMX8X). Check UART (Linux) to learn more about the corresponding UART names for your SoM.



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