Request for "system off" signal information

Technical Support
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1

I am currently using your module based on the i.MX6ULL (BSP 7.2.0) together with a digital acquisition board that controls several LEDs.
I would like to know if there is a dedicated digital output or signal available that indicates when the system is completely powered off, even though it is still being powered.
My goal is to ensure the system is fully shut down before cutting the main power supply, so that we can drive an LED to inform the operator when it is safe to to disconnect the power without risking any data loss.
Alternatively, is there a “power good” or similar signal that could be used for this purpose?
Thank you in advance for your support.
Best regards,

2

Hi, I’m the Toradex AI Assistant.

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Hello, and thank you for your question!

The Colibri iMX6ULL module does not provide a dedicated “power good” signal to indicate when the system is fully powered off, even if power is still supplied. However, you can implement a suitable solution using a GPIO pin to fulfill your requirements.

Recommended Solution: GPIO Power-Off Indication

You can utilize the Linux “gpio-poweroff” driver to control a specific GPIO pin when the system shuts down. This pin can be used to drive an LED, providing the operator with a clear status about when the system is safe to disconnect power.

Implementation steps:

  1. Enable the GPIO Power-Off Driver:

    • Ensure your kernel configuration has CONFIG_POWER_RESET_GPIO enabled. For BSP 7.2.0, this should already be available.
    • More info: GPIO Power-off documentation

  2. Device Tree Configuration:

    • Add a node in your device tree similar to the following (swap the GPIO and settings as needed for your application):
      gpio-poweroff {
    compatible = "gpio-poweroff";
    gpios = <&gpio3 23 GPIO_ACTIVE_LOW>;
};
    • This will drive the selected GPIO (for example, GPIO3_IO23) low when the system is shutting down.
    • After the system’s shutdown sequence finishes, this GPIO will change state (e.g., turn on/off the LED), indicating that it’s safe to disconnect power.

  3. Wiring:

    • Connect the selected GPIO to your LED (through appropriate resistors) or to external control circuitry as needed.

  4. Carrier Board Power Control (Optional):

    • If you are using a Toradex Evaluation Board, the power-on/off controller (LTC2954) has a FORCE_OFF# input. You could use the GPIO-driven signal and route it to this input for further automation.
    • More about this: Evaluation Board Power control

Summary:
There isn’t a native “power good” output on the iMX6ULL, but the Linux gpio-poweroff driver allows you to generate a safe-to-power-down indication through a standard GPIO pin.

If you need further details on setting up the device tree or choosing an appropriate GPIO, please let me know!

Best regards,
Toradex AI Assistant.

3

Hi @idir!

The answer given by the AI is partially correct. As far as I know, we don’t have a signal that indicates whenever the system is powered off even though it continues to be powered. It would need to be implemented by yourself.

That being said, the setup in the article that the AI recommended (GPIO Power-off) is outdated and, after some tests, it seems not to work. I already talked to the responsible team to fix the documentation. For now, we don’t have a way to do the power off the way you want.

A possible workaround would be using the command shutdown with some kind of switch to power off the board after the “software shutdown” is completed.

Best regards.

4

Hi lucas_az.tx
Thank you for your feedback.
Indeed, we were considering using a GPIO to handle a push button that triggers our script to perform a software shutdown. However, the issue remains that we don’t have a reliable way to know when the system has fully completed the shutdown process so that we can safely cut the power.
Do you happen to have any suggestions or best practices to detect the actual completion of the shutdown?
Best regards,

5

Hi @idir!

You could use an LED (soldered on the board or external) and a GPIO pulled up. This way, you would know whenever the system finishes its shutdown (the GPIO would go down and the LED would turn off).

I think this is a “simple” way to implement the shutdown detection.

Best regards.