This feature applies to MTCDTIP2 devices.

The supercap feature allows the device to perform an orderly shutdown of the CPU if power goes offline. This prevents loss of data.

Currently, the system waits up to 3 minutes for the supercap to charge during boot.

The 3 minutes is configured in /etc/default/mts-io:

# Supercap Feature
# Do not let boot proceed until supercap is full.
# Prevents loss of data when power is out.
SUPERCAPFULL=1
# Maximum wait time for SUPERCAPFULL
#
SUPERCAPFULL_MAXWAIT=180

If SUPERCAPFULL is not set to 1, the wait is skipped.

If power is lost and the supercap is sufficiently charged, a graceful shutdown is attempted. But if the supercap is not charged enough, the device may run out of power before shutdown is complete, and data could be lost.  The supercap should always be able to charge in less than three minutes, and this is done before user programs are initiated during boot.

NOTE:  It is possible custom code that executes too slowly in shutdown could cause a data loss. You should test any code you write that executes during shutdown to ensure that there is not a performance bottleneck. More specifically, a bottleneck that will prevent shutdown from completing before the supercap runs out of power.

Firmware Upgrades

Also, if the power is out, a firmware update will be skipped when doing mlinux-firmware-upgrade.

If the power is on, but the supercap isn’t sufficiently charged, the firmware upgrade will be delayed up to 3 minutes before attempted, so the supercap may charge.  This is not configurable.