Self-written firmware on the phone ala "Hello world"?

Question

ARM

And where to read some manual or article on how to make your own tiny firmware on your phone? Literally self-written: which, after turning on the phone, draws a circle or writes the text "Hello world!" and does nothing else. And on a modern phone like some kind of huawei or xiaomi.

Answer 1

Stomp on w3bsit3-dns.com/xda-developers with a search for your hardware (and each hardware will have its own troubles) and the twrp recovery project (it seems to be the most popular, if not the only open source), take its sources, delete unnecessary - profit.

Answer 2

w3bsit3-dns.com
1) You need to understand electronics (something like being an engineer);
2) You need to know the SI language (of course, not at the hello world level);
3) You need to know the Linux kernel (be able to configure and build it);
4) Know how to work with devices in Linux;
5) Download DataSheet to the devices of your phone (especially important - processor, video, display, etc.)
6) You need to unlock the bootloader;
7) Write your own loader;
8) Install the bootloader on the device (this is most likely the end, since in 99.99999 cases there will be a brick);
9) If tomorrow a meteorite destroys the Earth and you managed to launch your bootloader on the device, download the toolchain for arm and write the code of the simplest hello world. Start by initializing the devices. True, for a start it is better to display the dot on the screen, since fonts are needed for displaying on the screen - and this is + several thousand lines of code. Please note that such a "hello world" will be at least 10 thousand lines of code.
Good luck! If everything works out for you, be sure to publish an article on Habré !
PS: A thousand apologies - I forgot to add, you also need to know assembler!

Answer 3

It is impossible to write your own firmware for the phone, there are gigabytes of code, you will die before you can repeat it.