If on booting up, update.bin and update_desc.ini are placed on / of NAND,
update.bin has called with execv.
With placing "update.img" on USB stroage and insert to ASP , and select "System Update" will place these file onto NAND and reboot.
Next boot will run update working.
update.img is legacy zip format.
(it is some special , I could not make zip with WinZip,but open...)
Update.img(zip) has least two files "[somedir]/update.bin" and "[somedir]/update_desc.ini".
And it must be set password "xugameplay-snk"
update.bin is normal ELF executable binary or any.
update_desc.ini likes below.
[DESCRIPT]=<Do packed script which execute USB/command.sh>
This update_desc.ini is testing , but it will work with more test.
stock UI's "system update" supports not only game unlock but any works.