Search found 754 matches

by Nemesis
Wed Jun 12, 2019 10:58 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 9
Views: 265

Re: Designing a cooperative-threaded scheduler for an emulator

I don't have time to do this justice right now, but I'll get back to you on this soon. My problem here will be reducing my comments from book length. When I designed Exodus, I deliberately took different approaches on a lot of things, with the threading and execution models being no exception. I can...
by Nemesis
Fri Jun 07, 2019 1:06 pm
Forum: Megadrive/Genesis
Topic: 68K cycle timing test ROM?
Replies: 10
Views: 469

Re: 68K cycle timing test ROM?

It originated from a guy on http://www.atari-forum.com. I'm not sure he really maintains it anymore, but he's still active there. You can find him in this recent thread talking about it: http://www.atari-forum.com/viewtopic.php?t=36648
by Nemesis
Wed Jun 05, 2019 7:03 am
Forum: Megadrive/Genesis
Topic: 68K cycle timing test ROM?
Replies: 10
Views: 469

Re: 68K cycle timing test ROM?

All that said, I see the Microcode analysis ( http://gendev.spritesmind.net/forum/viewtopic.php?f=2&t=3023 ) as the way forward. Reading the microinstructions tells you what you need to know regarding cycle timing. I hope to extract simple, verified data tables at the end of that process to make thi...
by Nemesis
Wed Jun 05, 2019 7:00 am
Forum: Megadrive/Genesis
Topic: 68K cycle timing test ROM?
Replies: 10
Views: 469

Re: 68K cycle timing test ROM?

Kinda. If you want to be able to verify perfect cycle accuracy for all bus timings for all instructions, you're out of luck. I did work on making one that measured bus timings within an opcode for particular sets of instructions, but getting repeatable, stable results out of it while avoiding infini...
by Nemesis
Tue May 28, 2019 12:18 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 41
Views: 3112

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

I managed to track down a pdf of that "Microarchitecture of VLSI Computers" book that ijor mentioned. It has a lot of VERY interesting material on the 68000, much of which I haven't seen anywhere else. This book is a trade journal of sorts, being a compilation of papers presented at the "NATO Advanc...
by Nemesis
Mon May 27, 2019 4:58 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 41
Views: 3112

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

I was going to make my next big post on how microinstructions are addressed and encoded, but before that I decided it was important to start with a primer on understanding the CPU schematic diagrams. It's taken longer than I thought to write this part up, so I'm going to post it now and cover the 68...
by Nemesis
Wed May 22, 2019 3:56 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 41
Views: 3112

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

Well I may as well start to share what I've been working on. For the past few weeks I've been banging my head against my computer trying to write a simulator for galibert's netlist. ... Great work! I'm interested where this ends up. It'd be fantastic to be able to have something like that working. ...
by Nemesis
Wed May 22, 2019 3:41 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 41
Views: 3112

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

I've finally completed the microcode transcription from the 68000 patents. It was slow and boring and took forever, but it's done now thank goodness. My primary sources were EP0019392B1 and US4325121 . Hopefully some of you will find the result useful. Now that the data is in a clean digital form, i...
by Nemesis
Fri May 17, 2019 11:42 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 41
Views: 3112

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: 41
Views: 3112

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: 41
Views: 3112

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: 41
Views: 3112

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: 41
Views: 3112

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: 41
Views: 3112

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: 41
Views: 3112

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 ...