TS-TPC-7990 Sleep mode

The TS-TPC-7990 implements a very low power sleep mode using the onboard supervisory microcontroller. This allows powering off the i.MX6 CPU entirely. While in this mode the entire board will use about 6 mW for resistive or 26 mW for capacitive touch screens.

The board can be woken 2 ways:

• Timer - sleep mode requires specifying an amount of seconds to sleep (up to 16777215).
• Touch - The touch controllers are kept powered on while in sleep mode.

The sleep mode can be entered at a low level calling "tshwctl --sleep 60" to sleep for 60 seconds, but this typically should not be called directly. This would be equivalent to disconnecting power while booted which can cause data loss.

The Yocto, Debian, or Ubuntu distributions use systemd to manage shutdown. When systemd shuts down it will call all executables in /lib/systemd/system-shutdown/. Create a script silabs-sleep in this directory with these contents:

#!/bin/bash

tsmicroctl --sleep 60

And make it executable:

chmod a+x /lib/systemd/system-shutdown/silabs-sleep

Now the board will sleep immediately following a shutdown. It is safe during the sleep mode to disconnect power.