XT/370 microcode

On Mon, Mar 12, 2018, 05:13 Dave Wade via cctalk <cctalk at classiccmp.org> wrote: One Motorola chip was the custom one, the other was normal (as indicated by mask code). There was also an Intel math co, presumably derived from 8087. I used to have an AT/370, which had the same chipset, but I was never able to obtain the software. I very strongly suspect the modified 68000 and 8087 have more than just microcode differences, and that full reverse-engineering of the die would be necessary to accomplish anything useful with the microcode. Neither chip was designed to be a general-purpose microcode engine; both were very heavily tailored for their exact visible architecture, and 370 architecture is enough different that it couldn't be implemented by microcode only changes with no data path changes; the microcode ROMs and PLAs just aren't big enough to work around the data path issues.