Re: Shutdown vs. Restart

Marion, 2025-03-22 20:07:

[...]

AFAIK, there are also low-power data-collection hubs in modern Androids
which are actually processors that are independent of the main SoC which
collect data from sensors (accelerometer, gyroscope, magnetometer, etc.).

These exists since the beginning of Android. The whole mobile network
section including GPS and many other sensors is a computer on its own.

[...]

In fact, some hardware is always powered, AFAIK, given all Androids (AFAIK)
can charge even when the phone appears to be powered off and some have
always-on sensors (like accelerometers) which operate in very low-power
states (as likely do real-time clocks which keep track of time even when
the main OS is off).

Depending on the device there is also some indication for the charge
process even when Android is shut down. This is also supported by quite
old devices like some older Samsung smartphones or tablets which display
a battery symbol when charging even when the device was shut down.

But this does not mean, that Android itself is still running in this
state. This only requires some simple firmware function to display a
charge state on the display.

As I alluded to, there's an in-between "bootloader mode" or "fastboot mode"
(which is actually a communication protocol) which is a distinct state from
the reboot/restart modes as it provides low-level access to the firmware.

"Fastboot mode" is the state, where the firmware accepts "fastboot"
commands. "fastboot" is a commandline tool and part of the Android
developer tools. For example you can use fastboot to unlock the bootloader.

See here for details:

<https://android.googlesource.com/platform/system/core/+/master/fastboot/README.md>

The "bootloader mode" on the other hand is usually intended to install
new firmware via USB. You may also have some kind of recovery software
which will start first and allows you to do some diagnostics or wipe the
memory. This may be activated by some key combinations during startup.
Many devices enter the recovery when pressing Power + Volume up during
startup. With TWRP (Team Win Recovery Project) you get a quite powerful
toolset which allows to install OS images, do backups and so on.

Also see:

<https://en.wikipedia.org/wiki/TWRP_(software)>
<https://twrp.me/>


--
Arno Welzel
https://arnowelzel.de