@witnessmenow: It is a LOT of info, about the whole project.
What especially do you want to know?
First thing to know,...
The original "OSDSYS" *, searches for an official OSDSYS-Update (on MC and on some models also HD), which is MagicGate-encrypted.
If this Update-File is found, it decrypts and executes it as a "OSDSYS"-Replacement (which also means, this replacement must initialize the hardware on its own).
* (I assume Sony means "On Screen Display" for OSD and System for "SYS". That is the easiest explanation.)
The original OSDSYS is placed in "rom0:/" (without quotes).
PS2-Versions can differ between:
- MagicGate-Region (different en- & decryption) --> See the last two digits in SCPH-Number on the backside, of your PS2.
- PS2-Version (most of the time you can see it from the first two digits + sometimes a letter, after all digits)
- PS2-Revision (same Version, other motherboard-revision)
- ...some other things,...
From what we know, the OSD-update from MC/MemoryCard is available on EVERY console (regardless, of the PS2-Region, PS2-version and so on...)
OSDSYS searches for an OSD-update on mc in:
x = Number, of the MC (SLOT1 [mc0], or SLOT2 [mc1])
? = Region-Letter (...see FMCB-Tutorial... )
So,... That is the basic and beginning to know...
If you want to know, how the embed-process works (to create a valid encrypted "KELF"/Krypto-ELF/encrypted ELF), just ask but that is much more complex.
The easiest way to explain:
FMCB uses pre-encrypted files (thought, it was from "erom0:", or is there an "erom1:"?) to inject its own code to a section, where free not encrypted space is available.
This is necessary, to get a valid encrypted ELF-Header.
Well,... This is the basic how FMCB gets started, but I'm nbot sure, if that is, what you wanted to know.
Probably you also meant, how the hacked OSD shows up, which is something completely different (part of FMCBs Code and has nothing to do, how FMCBs loader itself starts.)
Btw: If someone finds a mistake, please correct me.
If I made a typo, which not leads to wrong info, you can have it. lol
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux