We also had decoded the 386's match-decoder PLA, so we knew roughly the locations of different opcodes were in the microcode itself, which was very helpful. Some opcodes have very specific operands, so would have unique field references. Some forms only operate on EAX/AX, for example, so if you find those instructions you have a hint of how the AX register is encoded as an operand.
replyOther instructions like PUSHA and POPA are implemented as loops that iterate by incrementing the fields corresponding to registers - and we know in what order they operate.
Bit by bit, relation by relation, you can puzzle out the format of the microcode. Of course, this is glossing over the enormous added complexity of protected-mode operations. This was a herculean effort by reenigne, and I don't think it is hyperbole to call it one of the more impressive human achievements I have witnessed in my lifetime.
The actual output of microcode disassembly is just a text file - a line of code for each microcode word, in essentially a a new dialect - a type of static assembly language. reenigne had to invent names for a lot of things, that will now become the official names of these things, unless Intel ever decides to speak up and make corrections.
replyThat language can then be translated into Verilog, and has been.