Automatic Power-On Behavior for i.MX8MP with overtemperature

[Marco_Savo]

I am using a congatec SMARC module with a imx8mp processor.

To clarify our requirements:

When the temperature sensor on the SMARC module reaches 105°C, the system powers off.

Currently, the system requires a manual power cycle to restart.

I would like to modify this behaviour so that the system automatically powers back on when the temperature falls below the trigger threshold.

We found references suggesting that this behaviour could be modified in the SCFW (System Controller Firmware). However, the SCFW firmware is not used for the i.MX8MP processor.

The boot sequence for the i.MX8MP is as follows:

BootROM → SPL → BL31 (ATF - ARM Trusted Firmware) → OP-TEE (Optional) → BL33 (U-Boot) → Linux kernel.

Based on our understanding, potential areas to address this behaviour include:

1. a) Modifying BL31 (ATF).

         Adjusting settings within the SNVS (Secure Non-Volatile Storage).

1. b) Configuring the PMIC PCA9450C present on the SMARC module to enable auto-power-on.

If the PMIC configuration is the correct path, could you provide documentation or details on configuring the PCA9450C for automatic power-on?

Or, do you have a better solution?

[Marco_Savo · Accepted solution]

I ended up setting a wake up alarm, and adding a service to set it up just before the shutdown. So each time the system would be triggered a power off etc. the alarm will be triggered. Better than nothing.

echo +120 > /sys/class/rtc/rtc1/wakealarm

[LFGP]

dear Marco_Savo,
to modify the BL31 is not an option.
your second option is not posible due you have to assert the PMIC_ON_REQ in order to start the power-on sequence it hasn't an auto power-on.
You could use a FPGA to assert the PMIC_ON_REQ signal.