Search found 746 matches

by Nemesis
Fri May 17, 2019 11:42 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

The US4325121 patent is the main one I'm referring to right now, with the appendices that list microinstruction details. While things changed in the final product, enough things should match up to allow me to correlate proper names for various registers/microinstructions, while also serving as a san...
by Nemesis
Fri May 17, 2019 1:59 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Thank you very much for your help. Yep, it sounds like my image tracks with what you just described. Thanks for clearing up the meaning of each layer, that makes a lot more sense now. You've answered some more of my questions already too, I was going to ask how you picked out the depletion mode vs e...
by Nemesis
Fri May 17, 2019 1:14 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Ahhh, just saw your reply! Took me an age to do the image work on my post. I'm reading through yours now and comparing to what I came up with, let me see if I was on the right track....
by Nemesis
Fri May 17, 2019 1:12 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I think I'm starting to get it. Here's a cross-section of an N-channel MOSFET for reference: http://nemesis.exodusemulator.com/M68000/NotGateDecode/mosfet.png The gate is defined by an insulated trace that runs over the top of the substrate. With an enhancement mode mosfet, when it's active power wi...
by Nemesis
Fri May 17, 2019 9:49 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Thanks heaps. I'll have a shot at building those tools tomorrow. I like to make things hard for myself and build all this stuff on Windows. So to confirm, the layers.svg file really contains all the important information, and it was manually created by yourself and quietust by tracing from the die s...
by Nemesis
Wed May 15, 2019 7:38 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I've created repos on GitHub for Schematic Explorer and the Annotated 68000 Schematic. If anyone wants to contribute, just fork the repo and submit a pull request.
by Nemesis
Wed May 15, 2019 7:20 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Looking forward to your work, Nemesis. I’m actually going to be starting on my own 68K HDL project for a personal project. If I find anything I’ll let you know. I’ve tinkered with the idea of taking the schematic you’ve posted and the text description of it and writing an program that searches for ...
by Nemesis
Wed May 15, 2019 7:14 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I've had a crack at annotating the physical location of the internal registers on another layer: http://nemesis.exodusemulator.com/M68000/SchematicAnnotation2.png This is primarily based on the work Gigasoft did , and I've used the register names he used. The annotation it isn't complete, as I got a...
by Nemesis
Wed May 15, 2019 4:41 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I've done another quick update to the schematic explorer. I've also completed a quick initial transfer of the annotations from the "official" die layout. Here's the original image: http://nemesis.exodusemulator.com/M68000/chip68k.jpg This was provided by Motorola about a billion years ago. It shows ...
by Nemesis
Wed May 15, 2019 2:34 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I've just updated the schematic explorer to fix some transformation issues, as well as improve the speed for updating the line scaling. If anyone's downloaded the previous build, I'd recommend moving to the updated one.
by Nemesis
Tue May 14, 2019 5:09 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Hey ijor, thanks for contributing. I'll have about 1000 questions for you I'm sure, so don't go anywhere! :) A lot of important information is contained in the microword descriptions in Appendix H, but they're borderline illegible, and very difficult to work with in their current form, They are not ...
by Nemesis
Tue May 14, 2019 4:48 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

Great write up Nemesis, thanks! I look forward to the next one. Over the past week I've been pouring over the netlist on Oliver's website trying to wrap my head around how this stuff works. I found some discrepancies between his schem.txt and schem.svg, emailed him to ask if indeed there was someth...
by Nemesis
Wed May 08, 2019 6:47 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 32
Views: 882

Re: I'm officially building a microcode-level 68000 core

I'm going to start write-ups on what I've learned so far, as I've been able to digest and document it. This should serve as a bit of a "microcode 101" introduction to the Motorola 68000 for others, and a reference for me when I inevitably forget half of what I've figured out in a week's time. For a ...
by Nemesis
Tue May 07, 2019 12:42 am
Forum: Exodus
Topic: Active Disassembly
Replies: 13
Views: 1009

Re: Active Disassembly

Those kind of structures are the ones that Active Disassembly in Exodus is designed to handle. You will need to follow a jump table like that through at least once before Exodus can even attempt to scan past it, but if you have a table with, say 20 entries, once you've hit around 5 of them, I'd expe...
by Nemesis
Tue May 07, 2019 12:18 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 87
Views: 1905

Re: Questions on writing a new Mega CD emulator

Dumb question but: isn't the spiral at a physical level basically just a long string of bits? Is there any reason for a preservation format to store a disc as anything other than those raw bits? (even with uncorrectable bits since, erm, that's precisely what the error correction scheme in the stand...