See the top level README file for more information on documentation and how to run these programs. Derived from bootloader05, this is a very simple bootloader. Instead of the sd dance (see toplevel README), this makes life a bit simpler and greatly reduces physical wear and tear on the sd card socket. Do the sd card dance one more time with kernel.img. Get some sort of serial solution to connect a dumb termial program with xmodem capabilities to the uart on the raspberry pi. (see the toplevel README for more information). The difference between bootloader05 and bootloader06 is that I made it more lean and mean either it works perfect or it bails out, I dont know or think the NAK stuff was working anyway. The whole xmodem receiver is in a loop so you should be able to try again without power cycling the board. I use minicom and it uses lrzsz to do the xmodem transfer and there is a delay after the transfer before minicom gets control again so I added a delay at the end before branching to the application so that no uart output is lost, in theory...Your favorite tools may give you a different experience. You take the .bin file of your test program, assumed to be built based on address 0x8000 and less than 0x200000-0x8000 bytes in size. With uart connected to a terminal 1) power off raspberry pi 2) power on raspberry pi 3) use xmodem to transfer binary file Repeat for each new program to test This bootloader sits at 0x200000 so that you have 0x200000 bytes to develop with. And that way if you like your program you can just copy a .bin version to kernel.img on the sd card and use it. It is easy to change this starting address, see the source for more. bootloader01 uses .hex files, bootloader02 through bootloader06 use .bin files, .hex files wont work. Consider bootloader01 and 02 to be obsolete. I normally do not deliver binaries. In this case I have included all of the build files so that you can at least get started without having to build the bootloader. Backup whatever kernel.img file you are using and replace with the kernel.img file in this repo (on your sd card).