I appreciate the reply. The complete datasheet for the Raspberry Pi is NDA locked. There is no documentation available for the majority of the die. As a simple high level reference the YT channel Electron Update and his respective blog have images of the decapped die where you will see the majority of it is dedicated to its original application as a TV tuner box. There is a partial datasheet for things like serial peripherals, but the registers level hardware outside of the ARM core are undocumented.

X86 has been mostly open up until the end of the Core Duo era. This is how Libreboot exists, but I believe Leah still had to reverse engineer the first generation intel management engine API ("Vpro" or whatever they called it). Indeed I have 2 machines running completely open source. One is on Gentoo and has complied itself from scratch including its bootloader, as a project a few years ago. True, the architecture for x86 has evolved, and to my knowledge, is undocumented in its entirety, especially stuff like the ALU configuration. We are on the precipice of RISC-V. The first server class machines running exclusively on RISC-V already exist in the wild. This will eventually make both x86 and ARM obsolete. By open sourcing the instruction set architecture, the dominance of exploitation in our current era will fade into proprietary blocks on the edges of the die and these should be easier to isolate or reverse engineer at the community level.

The x86 bootloader is indeed a major current issue, but just 2 weeks ago AMD released the OpenSIL project which is the open source release of the full initialization API for their current hardware. This release is the death knell for proprietary bootloaders. If Intel does not respond in kind very soon, it will be completely irrelevant in the server and professional space. There is no other way to address the open CVE's for the Intel Management Engine. Within the next decade, proprietary hardware will look like the medieval era of feudalism as much as a Nokia 3310 looks prehistoric to our current devices.