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From: "Carlos E.R." <robin_listas@es.invalid>
Newsgroups: comp.mobile.android
Subject: Re: is my phone ON or is it OFF?
Date: Thu, 2 May 2024 23:59:35 +0200
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On 2024-05-02 13:43, bad💽sector wrote:
> On 5/2/24 02:17, Carlos E.R. wrote:
>> On 2024-04-27 11:16, Theo wrote:
>>> Jörg Lorenz <hugybear@gmx.net> wrote:
>>>> On 25.04.24 15:55, Frank Slootweg wrote:
>>>>> Jeff Layman <Jeff@invalid.invalid> wrote: [...]

....

>>>> Bullshit! The OS is not booted when the Android is turned off.
>>> 
>>> AIUI it is, kind of.  When you plug in the charger with the phone
>>>  off, the phone starts.  The bootloader then launches the Android
>>> kernel with the flag androidboot.mode=charger
>>> 
>>> Instead of doing the full Android boot, that causes the kernel to
>>>  launch a charger UI application that shows your battery
>>> percentage on the screen or an animation (which comes from files
>>> on your OS partition).  The charger app doesn't allow you to
>>> otherwise interact with the phone and other services like the
>>> radios aren't running, but the SoC is booted and running 
>>> software. The SoC is also doing standard power management, ie the
>>> charging process here likely looks very similar to charging when
>>> the phone is turned on (because it is, in essence).
>>> 
>>> The full OS services are not running, but the Android kernel and
>>> the charger app is.
>>> 
>>> Theo (usual caveats: my understanding may be out of date,
>>> different vendors may do their own thing, etc)
>> 
>> 
>> Hum!  That's the best explanation I have seen so far. Thank you. It
>>  explains things.
> 
> 
> Like your compuer, it's sleeping with one ear (and maybe eye) open.

Low power processors can do things like switch off circuitry, or stop
processing completely till some external event happens.

This is used in circuitry that runs on batteries for months, like the 
speed meter of a bicycle. If the wheel doesn't turn, the processor and 
everything sleeps, except the turn counter.

Well, this is the same idea: boot a different image that only powers up 
what it needs in order to track battery power and charging.

Doable.

-- 
Cheers, Carlos.