But the VideoCore IV is kind of a weird vector processor, there's still a lot of official documentation we don't have, there are those ring buffers, you have to

But the VideoCore IV is kind of a weird vector processor, there's still a lot of official documentation we don't have, there are those ring buffers, you have to wake the— Oh, you meant the ARM? Oh, my, no, the Pi doesn't boot from that. The ROM loader starts the SDCard and loads BOOTCODE.BIN to the VC4 with cache-in-RAM mode; that's its equivalent of the bootblock. The ARMv6 isn't even turned on until the next chain later (used to be two, from memory?). So, you know, if you fancy a much more fun, more advanced, challenge, it's right there waiting for you, under the crust. Have fun. Let me know if you find a diagonal vector addressing mode or a good way of shuffling words! <grin> (PS: There is actually someone at Broadcom working on open-source firmware for the Raspberry Pi, or was last I checked. They're going to have to rewrite it: the ThreadX RTOS they used is commercial. But he has firmware documentation, at least. You have… some of it.)