Booting failure happened sometimes while repeating Power ON/OFF test. When the booting failure happened, BOOT_MODE is read serial download by DDR Stress Tool. However, actually BOOT_MODE is internal boot by boot strap. The booting device is NAND.
for "repeating Power ON/OFF test" it is necessary to verify that after power off
all power supplies were fully discharged, then turn power on. Otherwise this may violate
power up sequence.