PMIC imx8mq debugging board power resets

[elcfd]

Hi,

I have been developing an OS using Yocto on a development kit with the IMX8MQ. The image runs fine and I have not had any issues.

When I started to use our custom board with the IMX8MQ and same image I am seeing two issues;

* Sometimes the board boots and then bootloops before the login prompt is reached. This only seems to happen from a warm start (i.e. the power was applied shortly after the board had been switch off from running previously). If the board is left a while and then turned on it does not bootloop.

* With the OS running but under heavyish load the board will lose power and reboot itself.

When this issue occurs nothing is printed to dmesg or journalctl and I cannot see a kernel panic over serial. This seems to be a power management issue particularly with the design of the custom board.

So I have decided to try and debug the PMIC. When this issue occurs I interrupt u-boot and read the PMIC's i2c registers. However, the i2c registers of the PMIC are the default ones and it does not seem that the PMIC statuses are persisting over the power off and on.

How can I see the PMIC's registers/reason for the power off and on?

Thanks,

Charlie

[elcfd]

Thanks we tracked this down to our custom PCB design and having a regulator which was cutting out under heavy cpu load. Increasing the regulator's tolerance solved the issue.

[igorpadykov · Accepted solution]

Hi Charles

you are right, this may be caused by power supplies. One can check them using

Maximum ripple voltage requirements defined in Table 8. i.MX 8MDQLQ power/decoupling
recommendations, sect.3.6. Power connectivity/routing  i.MX 8MDQLQ Hardware Developer’s Guide

During power loss there may be no option for debugging.

Best regards
igor