Opcodes to be implemented are found on x86asm.net, where proc_start is =< 4. Most peskier lower details are found in this original datasheet from 1993, and will be implemented as long as it is feasible.

The aim is to create a Verilog implementation, test it against a real i486, benchmark and finally create ICs - both low-level pin-compatibles and a higher level DIP package.

Q/A

• Will it go beyond the i486?
  • I do not know, most likely additional features will be implemented, and pesky bugs will be eradicated.
  • The primary reason I stick to the i486 is to avoid legal trouble, and to make it a whole lot simpler for me.
    • Doesn't mean features from the Pentium will sneak in as they too lose patent protection, however.
• Will it be detectable/differ from the real deal from an OS point of view?
  • For CPUID, VendorID will be TrulyFreeCPU, the rest will be as provided by a real i486 for compatibility.
  • You will be able to use an additional custom instruction to run in "compatibility mode", reverting the VendorID and disabling eventual non-standard i486 features.