Originally Posted by Mackx
10: hwclock -s -u
I assume that this command stops the cpu clock, stalling all processing. It will presumally also trigger a special DRAM refresh mode to preserve the ram-content. Since the cpu stopped, power consumption is very low. An external processor (I assume there is a separate display processor that controls the eInk-screen, pre-processes the wacom layer events and checks the keys.) can get the main cpu out of the low-power mode by triggering an external interrupt on the main cpu.
You're close. The device is put into low power mode after 5 seconds of idle by a call to idle.sh. There is a standby microprocessor in the device which controls power to various components, key input etc (it does not drive the display though). The hwclock-line is called when operation is resumed to sync the Linux clock as it does not get updated while in idle mode.