Search found 760 matches

by Nemesis
Sat Aug 10, 2019 1:49 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 9320

Re: Questions on writing a new Mega CD emulator

Unfortunately the data is never passed on when it's in that mode. I'm on my phone and can't look things up properly, but IIRC whichever asic gets the raw data stream from the laser also exposes the TOC data, and it never passes the data on when it's doing TOC decoding. Only way I could get at that d...
by Nemesis
Sat Aug 10, 2019 1:42 pm
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 43
Views: 5446

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

Just doing a quick post to say I haven't forgotten about this or abandoned it. My wife gave birth to our fourth child about two weeks ago, and leading up to that I needed to devote extra time to getting ready and helping my wife, as well as getting things squared away at work. I'll be turning my att...
by Nemesis
Wed Jul 03, 2019 3:07 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 14
Views: 1490

Re: Designing a cooperative-threaded scheduler for an emulator

I think this discussion lack clarifying objectives. Is it "cycle accuracy" what are you aiming for? Is it speed? Perhaps a mix of both? And then what is “cycle accuracy” really?, as its name says should be that at the end of every cycle the chip status is the same as emulator status, but I bet no e...
by Nemesis
Thu Jun 27, 2019 12:12 pm
Forum: Video Display Processor
Topic: hv counter details
Replies: 2
Views: 441

Re: hv counter details

It's mostly covered by Sik, but I'll add a bit more detail on a few points. The H counter is simple enough, here are the notes on it from my Emulator: // The internal hcounter is 9-bit, and the external hcounter is 8-bit. The upper 8 bits // of the 9-bit internal hcounter are used to build the 8-bit...
by Nemesis
Mon Jun 24, 2019 4:57 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 14
Views: 1490

Re: Designing a cooperative-threaded scheduler for an emulator

For illustrative purposes, here's an annotated profile snapshot of Exodus while executing a Mega Drive ROM: http://nemesis.exodusemulator.com/Exodus/ExodusThreads.png I've annotated the threads that are used for particular tasks of interest in red. You can see the 68000+Z80 thread spends almost all ...
by Nemesis
Mon Jun 24, 2019 4:37 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 14
Views: 1490

Re: Designing a cooperative-threaded scheduler for an emulator

Sorry, I meant to come back to this much sooner. A lot of good stuff has already been discussed so far. My reply is going to be a bit long, so apologies in advance. What started out as a simple reply has morphed into a kind of full introduction to the problem for the uninitiated. If you've already w...
by Nemesis
Wed Jun 12, 2019 10:58 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 14
Views: 1490

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: 1125

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: 1125

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: 1125

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: 43
Views: 5446

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: 43
Views: 5446

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: 43
Views: 5446

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: 43
Views: 5446

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: 43
Views: 5446

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...