A problem with all ARM system on chips is that they don't have any kind of standard like the PC is for x86. There's some work going on on that field but at the

A problem with all ARM system on chips is that they don't have any kind of standard like the PC is for x86. There's some work going on on that field but at the moment, each ARM SoC has their own conventions for booting. It is typical that there is a smaller ARM bootstrap core on the SoC that does the early boot process and kicks up the actual (bigger) ARM core(s) and then hands over control to a bootloader (like u-boot) or boots the OS using a device-specific bootstrap code. In other words: it would not be fun to do this using a RasPi (depending on your definition of "fun" of course). You would be spending lots of time with scarce documentation, dealing with practically no debugging aids and the only way to know if your code is working is whether a LED lights up and no way to debug failures. If you had a development board, perhaps you'd have JTAG or other debugging means available but I'm not sure if you can find this on a RasPi. You'd end up with very little transferable knowledge from this project. Of course, working with scarce documentation in a harsh early boot environment is a valuable skill in itself, but not the kind of stuff I'd voluntarily get into. This stuff is hard enough to do on a well documented, widely available platform like the x86 PC.