The issue was stumbled upon during environmental tests of a new design, loosely based on iMX6 smart device board.
Reboot instead of poweroff is always initiated on all the 3 boards available with both 1.2 and 1.3 silicon revision, when the processor junction temperature goes above approximately 93C, judging by embedded sensor data in /sys/class/thermal/thermal_zone1/temp. Other than this the tests are Ok, below the threshold poweroff is Ok, too.
The issue persists if the poweroff command is issued by directly writing to SNVS_LPCR register with memtool utility.
During the attempted poweroff the PMIC_ON_REQ pin drops low for approximately 3.8ms then goes high and a normal boot executes. VDD_SNVS_IN voltage shows a small momentary drop, but stays above 2.9V. PMIC interface signals have no other connections.
Thanks for the suggestions,
Sergey
Hi Sergey
i.MX6Q Sabre SD has "AUTO ON" feature described on schematic spf-27392 p.19
Schematics (1)
"Design files, including hardware schematics, Gerbers, and OrCAD files."
SABRE Platform for Smart Devices|NXP
One can try to implement "OPTIONAL: PMIC Power On Circuit" or similar depicted
on the same page.
Best regards
igor
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Hi Igor
Thank you for settling me onto the right way.
Actually, my design has no any "AUTO ON" features, but following your advice I noticed leakage through power button sensing diode (D4 in the schematic you refer to). At high temperature this leakage grows enough so as to pull ONOFF pin voltage down to approximately 2V. Although I didn't observe any futher drop-downs in ONOFF voltage during poweroff attempt, the leakage evidently stands behind the issue. I healed the boards just by removing "D4" . Next I will try to look for a diode with smaller leakage to restore power button sensing.
Thanks and regards,
Sergey