Search found 196 matches

by Huge
Fri Jun 14, 2019 3:02 am
Forum: Megadrive/Genesis
Topic: Designing a cooperative-threaded scheduler for an emulator
Replies: 11
Views: 700

Re: Designing a cooperative-threaded scheduler for an emulator

I have never done low level programming and I'm completely out of my depth here, but one time I contemplated, just for the sake of argument, how emulating a multiple devices down to a cycle could work... Very possible that I'm completely wrong here, but couldn't you keep an array of variables in a c...
by Huge
Mon Jun 10, 2019 8:46 pm
Forum: Mega/SegaCD
Topic: Japanese MegaCD BIOS 1.00C
Replies: 1
Views: 163

Re: Japanese MegaCD BIOS 1.00C

I remember seeing that "pre-retail" unit. Glad to see the boot rom got dumped! It also predates the official rom identification number (not marked as EPR/MPR-14088x). For the record, EPR-14088B - ver 1.00g EPR-14088C - ver 1.00l EPR-14088D - ver 1.00o EPR-14088E - ver 1.00p MPR-14088H - ver 1.00S Th...
by Huge
Tue Jun 04, 2019 7:55 pm
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 789

Re: Bike shedding a new CD-ROM format

As I recall some PC protections used purposefully bad sectors, which got automatically "corrected" when dumping them. I don't remember the details, but this may be a problem if you decide to not store ECC. I should note that if you use the disc, or mount an image with the intact subcode data of a CD...
by Huge
Mon Jun 03, 2019 10:58 pm
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 789

Re: Bike shedding a new CD-ROM format

It's true that subcode can be generated, but if you generate them, why even bother trying to read them? And if you *assume* how the format looks based on the rules, then you'll overlook discs which do not confirm to those rules. Not that I can name any from the top of my head, but if we are using cl...
by Huge
Mon Jun 03, 2019 8:47 am
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 789

Re: Bike shedding a new CD-ROM format

Subcode reading is dodgy, even on the best drives. That is, you can't rip two of the same discs to identical CRCs.
by Huge
Sat Jun 01, 2019 6:20 pm
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 789

Re: Bike shedding a new CD-ROM format

This would be great, but what exactly would you use to rip in these formats? They are kind of pointless if nothing can create them. Don't forget that most data you want to rip is "unrippable" due to not only damage to the CDs, but also due to defective duplication, mastering errors, etc. There's a r...
by Huge
Sat May 18, 2019 9:20 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 6014

Re: Questions on writing a new Mega CD emulator

Mega CD specification doc is nice. No official Saturn CD format specification around, btw? ST-040-R4-051795 and tech bulletin #7 details those. It's nothing we haven't known before, though. It mostly details things like minimum LBA, the ISO9660 filesystems, sector frame sizes - all standard CDROM s...
by Huge
Sat Apr 20, 2019 2:37 am
Forum: Blabla
Topic: Where is your very first Megadrive/Genesis now?
Replies: 4
Views: 919

Re: Where is your very first Megadrive/Genesis now?

The first one has been sold for a Saturn a long time ago.

The second one, which is the one I bought from my own money, has been my primary unit for 20 years now. Over the years it was enhanced by a couple of mods and has been recapped.
by Huge
Mon Apr 15, 2019 1:33 am
Forum: Megadrive/Genesis
Topic: Compiling an emulator for enhanced Megadrive
Replies: 42
Views: 3217

Re: Compiling an emulator for enhanced Megadrive

There's little point to the "Tower of power" when a Saturn is better for all practical purposes. Still being a Genesis is part of the constraint. How about going backwards then: making something for the Saturn to run Megadrive games ? Obviously doing it in software alone would be near insanity, but...
by Huge
Tue Apr 09, 2019 7:55 pm
Forum: Megadrive/Genesis
Topic: Compiling an emulator for enhanced Megadrive
Replies: 42
Views: 3217

Re: Compiling an emulator for enhanced Megadrive

How does the C2 have 15bit colour? I thought it just had the external palette hooked up to double the entries from four to eight.
by Huge
Tue Mar 26, 2019 1:54 pm
Forum: Megadrive/Genesis
Topic: Space Herrier II and The Sprite Scanline Limit
Replies: 11
Views: 1109

Re: Space Herrier II and The Sprite Scanline Limit

Keio Flying Squadron does something like that, using sprites as a background. At one point (around stage 5 or 6?) it has a huge Ark that splashes onto the sea and you have to catch up with it. Normally the sea takes up all the backgrounds, and once you reach the ark, it's made up of sprites only. Th...
by Huge
Sun Oct 28, 2018 9:35 pm
Forum: MegaLD
Topic: MegaLD Dumping Project
Replies: 73
Views: 36528

Re: MegaLD Dumping Project

by Huge
Tue Sep 18, 2018 12:33 pm
Forum: Hardware
Topic: Some questions about Saturn HW
Replies: 25
Views: 5361

Re: Some questions about Saturn HW

Yeah, 14.318 / 4 = 3.579545 MHz and 17.734 / 4 = 4.43361875 MHz, the NTSC and PAL colour bursts, respectively. The PLL outputs them to the video encoder.
by Huge
Mon Sep 17, 2018 10:05 pm
Forum: Hardware
Topic: Some questions about Saturn HW
Replies: 25
Views: 5361

Re: Some questions about Saturn HW

Thanks for this complete answer ! So it could be possible to overclock the saturn but not without affecting video signal? No, the VDP2 generates the dot clock using the input clock / 4. If you over or underclock the system, it will display the wrong resolution and/or the wrong h/v sync and the imag...
by Huge
Mon Sep 17, 2018 1:04 pm
Forum: Hardware
Topic: Some questions about Saturn HW
Replies: 25
Views: 5361

Re: Some questions about Saturn HW

The SH2/VDP1/VDP2/SCU clocks are generated by a PLL (IC20), which uses 14.318MHz * 2 = 28.6 MHz in 352px mode. In 320px mode, it runs the frequency through a 1708/1820 divider to get 26.8MHz. SCU DSP runs at half of that. In PAL units it uses a 17,734 MHz crystal and it is run through a 910/1135 div...