Just a note to myself to keep useful info. Bakul Shah in freebsd-arm quotes R-Pi forum, but I failed to find original.

  1. Stage 1 boot is in the on-chip ROM. Loads stage2 in the L2 cache!
  2. Stage 2 is bootcode.bin. Enables SDRAM and loads stage3
  3. Stage 3 is loader.bin. Knows about elf format and load start.elf
  4. start.elf loads kernel.img (+ it is the main gpu code). It reads config.txt, cmdline.txt and bcm2835.dtb If the dtb file exists, it is loaded at 0x100 & kernel @ 0x8000 Else if disable_commandline_tags is set load kernel @ 0x0 Else if load kernel @ 0x8000 and put ATAGS at 0x100 See Issue 16 in https://github.com/raspberrypi/linux/issues
  5. kernel.img, is the first thing that runs on the ARM processor.

And more information on config.txt here