Custom code before second stage bootloader.

[Mikhail Zarzhevskiy]

Dear colleagues,

there is a need to do some manipulation with GPIO straight after power is ON.
Standart second stage bootloader takes hole 300ms before starts user app.
I've stucked for two weeks trying to find a way to squeeze my small GPIO cod in front
of the second stage bootloader (in the beginning of it).
There is only a pair of words about customer bootloaders in the API Guides , and my
level of Cmake and Make knowledge didn't let me succeed in using this hint )))
Which instructions can i use in the very beginning of the second stage bootloader?

I turn to comunity for a help in a form of some example of such implementation with
a minimum explanation of necessary environment , or, at least, for instruction where
i should look for this)))