<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Emulating a 68000 to emulate a 370?<div><br></div><div>At some point it starts to resemble the light 'hack' in an early big-bang theory episode:</div><div><br></div><div><a href="https://youtu.be/onZ4KMM94yI?si=AZGAKQr5QvL3yZrD">https://youtu.be/onZ4KMM94yI?si=AZGAKQr5QvL3yZrD</a><br><br>I mean I get it, but...</div><div><br><div dir="ltr">Ken</div><div dir="ltr"><br><blockquote type="cite">On Sep 12, 2023, at 16:46, Joshua Boyd via rescue <rescue@sunhelp.org> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><span>On 9/12/23 16:37, Dave McGuire via rescue wrote:</span><br><blockquote type="cite"><span>On 9/12/23 16:25, Mouse via rescue wrote:</span><br></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><span>Wasn't the XT/370 primarily made with 68000s with custom microcode?</span><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><span>[...] I'd love to see someone work out how to redo that on a newly</span><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><span>made board.</span><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><span>Since the 68K's control store is in mask ROM on the chip, I think</span><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><span>that would be a challenge.</span><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><span></span><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><span>I can't imagine that there would be any difficulty beyond possible lack</span><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><span>of documentation in reimplementing a 68k with writable microcode in a</span><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><span>modern FPGA.</span><br></blockquote></blockquote><blockquote type="cite"><span></span><br></blockquote><blockquote type="cite"><span> How I interpreted Josh's question was the modification of a 68K's microcode.</span><br></blockquote><span></span><br><span></span><br><span>I was originally thinking modify the microcode in the chip, but making a cycle accurate microcode compatible 68K in an FPGA to run altered microcode would also be cool. Extra cool if the FPGA's image was derived from a scan of the 68k silicon. Square the cool if that was then run through on one of Google's Open MPW shuttles.</span><br><span></span><br><span>I haven't dug into it too deeply, but I think that when people talk about emulating 68000s as part of, say, the MiSTer project, they are using a fairly high level emulation of 68000s, not something that is executing original microcode. I guess it would be interesting to know what is really happening there. Also how far down the accuracy hole the MAME 68k core goes.</span><br><span></span><br><span></span><br><span></span><br><span>_______________________________________________</span><br><span>rescue list - http://sunhelp.org/mailman/listinfo/rescue_sunhelp.org</span><br></div></blockquote></div></body></html>