RPi3 support

[profilernz]

I'm not able to get raspbootin working on a RPi3.
I get garbled output like:

### Listening on /dev/ttyUSB0     
��)c�c�

Any help or advice would be greatly appreciated.
Thanks

[Benjoyo]

The Raspberry Pi 3 has a 64bit ARM processor so this will not work (it's 32bit).

See here for a 64bit port of this bootloader: https://github.com/bztsrc/raspi3-tutorial/tree/master/14_raspbootin64

[mrvn]

The 32bit should not be a problem. Just don't load raspbootin as 64bit kernel. And you won't be able to chain load a 64bit kernel. The UART on the RPi3 is also at the same place as on the RPi2.

So I think what goes wrong is detecting the RPi model. I'm rewriting this now to use device trees instead of ATAGs which is more the standard boot protocol on ARM. I will close this when I can boot on my new RPi4 with the new code, which should test both 64bit cpus booting 32bit code and detecting the uart correctly.