See the top level README for information on where to find the
schematic and programmers reference manual for the ARM processor
on the raspberry pi. Also find information on how to load and run
these programs.
There are two programs here one is blinker05 and the other uart02.
The difference from their originals is the boot code. In attempt
to not care about where the gpu loads our program (so long as it is
not really close to zero), the startup code looks to see if we booted
at zero, if not, it copies the program from where it is to zero, then
branches to zero. Some linker script items were required to make this
work. First ram starts at 0x0000, that is where we are going to
copy our file. Second, the size of .text is added as a variable.
We can use this variable to connect to the startup code (vectors.s).
The bootcode for blinker05 had another modification, since the linker
is going to think that 0x0000 is the entry point it is going to make
the reset_handler variable contain some number like 0x0040, so right after
you start running that program it branches to zero which has who knows
what code, and you are stuck. That first instruction needs to be a
branch not an ldr pc of some linker filled in value.
11e7b38f4b