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
And more information on config.txt here