Follow-up to this note.

Dragan had asked me to do repeated power-cycle tests with different kernel versions using the patched dtb for #RockPro64 to make sure the kernel #oops wouldn't still be an issue.

I learned that cutting the power of the device could kill the #LPDDR4 #RAM. This is documented in the specification referenced on the RockPro64 wiki page for Micron LPDDR4 Mobile LPDDR4 Datasheet as stated on page 37 in Uncontrolled Power-Off:

An uncontrolled power-off sequence can occur a maximum of 400 times over the life of the device.

I never had heard about this before! Cutting power without shutdown can kill my RAM?

show dmesg and shutdown

To get all the debugging information I needed I wanted the system after booting to print dmesg to the serial console, wait a short time and then actually shutdown.

root:~# cat /root/bin/dmesg_and_shutdown.sh
#!/bin/bash
# a small script that outputs dmesg to serial
# console, waits 20 seconds and shuts down
dmesg > /dev/ttyS2
# show a message how to stop this script and wait 20 seconds
echo "Will shutdown in 20 seconds - to stop me call 'pkill dmesg_and_shut'" > /dev/ttyS2
sleep 20
echo "shutdown -h" > /dev/ttyS2
shutdown -h now
# a cronjob that runs after each boot
root:~# crontab -l
@reboot /root/bin/dmesg_and_shutdown.sh

powercycle the board

I took the time needed for a complete cycle of booting, showing dmesg, waiting and shutting down: well below 2 minutes.

To automate the power cycle I used an #esp8266 based power switch made by #Sonoff (Powr2) running ESP Easy (mega-20210503).

#ESPeasy offers a simple scripting language I used to powercycle after 120 seconds of being switched on:

On System#Boot do
 gpio,12,0
 gpio,13,1
endon

On button#button_state do
 if [blue_led#blue_led_state]=1
  gpio,13,0
  timerSet,1,2
 else
  gpio,13,1
  gpio,12,1
  timerSet,1,0
  timerSet,2,0
 endif
endon

On Rules#Timer=1 do
  gpio,12,0
  timerSet,2,1
endon

On Rules#Timer=2 do
 gpio,12,1
 timerSet,1,2
endon

Pressing the button on the Sonoff device toggles between:

• blue led off: timers disabled, relay on permanently
• blue led on: timers switch the relay off for 5 seconds, on for 120 seconds and then repeat

logging

minicom logged the serial output to a file.

Further down the #RabbitHole I went when looking at the resulting logfile…