Ultra low power initialisation results in reboot


We have made our own hardware based on the mangoh board and made a new yocto installation to fit our needs. Now the time have come for me to make sure that ultra low power is working, however, it seems that initializing ultra low power on our own hardware results in a reboot rather than a poweroff, whereas the same command on the mangoh board correctly shuts down and wait until the set trigger before starting again.

Any hints on how to debug this?

Kind regards


The only meaningful difference I get on the UART terminal when I do this on our own board where it reboots and the mangoh red board where it correctly powers off is the following lines (present on the mangoh board, but not on our board):

reboot: Power down
Powering of\FE

I haven’t been able to find which part of the kernel or image code is printing this line

Hi andcor,

Are you able to run the official Sierra image on your board and see any different?
And any chance relate to boot signal (PWR_ON / POWER_ON_N)?


I am able to run the default image and I see the same behaviour. On our hardware it reboots whereas on the mangoh board it correctly powers off.

I have debugged it down into the kernel/reboot.c and found that if I add some delay here the problems disappears. I haven’t been able to figure out which kind of race condition this delay is solving, but it seems it is a fix to our problem. It doesn’t feel good to leave it there, but the schedule of our project sadly doesn’t leave me much choice.

I have, by the way, also had a scope on the POWER_ON_N signal and that stays rock solid at a logic high level.

Thank you for taking your time to look into this.