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Image: Raspberry Pi Software flow-chat
The PiDesktop power control strategy ensures the main power is cut off only after the
Raspberry Pi has been completely shut down. This is important for the safety of the flash
chip and the filesystem of the Raspberry Pi board. Without this strategy errors can
occur, causing delayed file system checking or a situation where the system cannot start
up.
3.3
Real Time Clock (RTC)
Each time your Pi Desktop starts up it will connect to what is called a Network Time
Protocol (NTP) server and request the time.
If there is no internet connection the Pi Desktop utilizes the integrated RTC on the Pi
Desktop add-on board. This contains a battery powered clock chip that tells the
Raspberry Pi what time it is. To ensure accuracy the time will need to be set on the
system initially.
Note:
Installing the software package then rebooting the system will enable the RTC.
3.3.1
Adding a Real-Time Clock on Raspbian Jessie
The Raspberry Pi is designed to be an ultra-low cost computer; therefore the RPI
board itself does not include a battery for the RTC. Instead, the RPi is intended to
be connected to the Internet via Ethernet or WiFi, allowing it to update the time
automatically from the global ntp (nework time protocol) servers.
For stand-alone projects with no network connection, the Raspberry Pi will not
keep time when power is removed.
This section will explain how to add a low cost battery-backed RTC to your
Raspberry Pi to enable time keeping and introduce what the pi-desktop debian
package can do to sync time from RTC.
Raspbian Jessie (Systemd)
Step1: Adding a device tree overlay
You can add support for the RTC by adding a device tree overlay.