I would love to see a proper legal analysis of this. From what I recall, the closest thing to an answer I've received in the past is that you can not use the m

I would love to see a proper legal analysis of this. From what I recall, the closest thing to an answer I've received in the past is that you can not use the manuals to a modern x86 chip (or other part) to learn the instruction set. The use of any copyrighted material infects you project if the rights holder is particularly egregious about enforcement to that level. It's the same thing with the IBM PC BIOS reverse engineering. If you'd seen the BIOS manual, you couldn't work on the clone. I can't recall if that was purely seeing it or because the source code to the IBM BIOS was printed in the back of the manual. I know Intel, Microchip, and ARM have aggressively shut down any FPGA project that implements an instruction-level compatible core of x86, AVR, PIC, or ARM CPU. Intel seemingly hasn't gone after any of the 16-bit x86 core implementation, but I haven't seen an open source 386 or newer core.