Mac OS on a Sega Genesis? Yes!

[evildragon]

Ok, this has GOT to be the coolest thing I have done (besides my NES DVD player, but this is a SEGA forum)..

I have successfully booted Mac OS 7, on a stock Sega Genesis, equipped with a Sega CD, and a 32X. All 3 are being used for this project.

How does it work? Here's how!

First things first. The cartridge has some hardware that is required for this operation. A ROM to boot the Genesis (with a Mac ROM "clone"), extra RAM, an ethernet interface, and an IDE controller.. (only the most important hardware!)

Now, the Sega Genesis IS the core of the system, the 68k in the Genesis is literally running the Mac OS 7 operating system. But, how is the Genesis using the other hardware? Well, I did make a circuit I found online, to use a PS/2 keyboard, and a serial mouse on the Genesis.. so THAT helps a lot...

The 32X is running a program, that makes it act as a graphics card for the Genesis (yes, the VDP in the Genesis is doing nothing, just a black screen to give a "sync" to the 32X), with 15-bit colors (32 thousand colors). What is the resolution of this bad boy? 640x448. Ok, the 448 lines you probably understand, there is a hidden interlaced mode. But what about the 640 pixels in width? It's fake.. It's a "pseudo" 640px. What I mean, is it will show pixels the even pixels, then the odd. Like interlacing, but horizontally (obviously a TV can't interlace horizontally, that's why it's "pseudo")

The SegaCD is also running a program, which emulates the SCSI API, so Mac OS 7, can use the Sega CD as a regular 1x SCSI drive (well, there's a performance hit, and it's more like .8x).

Now, how about the sound? Joe literally couldn't wait for the samples of what Mr. 2612 could do. The FM channels are not working in Mac OS 7, because well, Macs NEVER had FM sounds (due to Apple vs. Apple). But, the 6th DAC, is functioning, and doing "ok". I say "ok" because I'm an audiophile, and frankly, I think it sucks.

Oh, and the ethernet interface? Yea, the Genesis is able to go on the internet.

Here are some screenshots of it running (this was before the IDE controller and before the 32X was even implemented yet, so it was running off the CD):
http://blackevilweredragon.spymac.com/sega/segamac1.jpg
http://blackevilweredragon.spymac.com/sega/segamac2.jpg
http://blackevilweredragon.spymac.com/sega/segamac3.jpg
http://blackevilweredragon.spymac.com/sega/segamac4.jpg

As it is now (with the ability to take screenshots, and with the 32X doing graphics, and with an IDE hard drive):
http://blackevilweredragon.spymac.com/segamac1.jpg
http://blackevilweredragon.spymac.com/segamac2.jpg
http://blackevilweredragon.spymac.com/segamac3.gif
http://blackevilweredragon.spymac.com/segamac4.gif

Here is a video clip, of it running, when I first tested the 32X and IDE implementation (i had the Genesis attached to my LCD monitor via RGB): http://www.spymac.com/upload/gallery...nninghd32x.mov

And now, here's some audio samples. These first two, are when I was testing my 2612 program. This was before Mac OS was even booting.. Here you hear the 2612 doing some, should I say, interesting music. The first one, I have no idea why it went crazy. I think you literally hear the 2612 loading the patches (my bad programming probably--a bug) (oh, and those two clips all use channels 1 to 6 as FM, using the same patch, so you get 6 note polyphonic):
From a Genesis 2:
http://blackevilweredragon.spymac.com/gen2612test.mp3

From a Genesis 1:
http://blackevilweredragon.spymac.com/2612sonata.mp3

This sound clip here, is what it does today, when you turn it on.. First you hear the 2612 using FM sound to mock the Mac "choir" sound (from 68k macs), and then you hear the 2612 using DAC sound to play the REAL choir sound:
http://www.spymac.com/upload/gallery...50_segamac.mov

And the grand finale, the one that Joe almost begged me to record , the 2612 playing a song, through the 6th channel DAC (to hear what it can REALLY sound like):
http://blackevilweredragon.spymac.com/2612vanhalen.mp3

(since the audio quality of that is sooo low, and not even in Stereo, i'm sure it's ok to have that full song.. if not, i'll clip it and make it shorter)

----------------------------

Oh, and this is being typed on the Genesis right now, on Netscape 4, on Mac OS 7...

[Ski_Dude_Andy]

wow thats amazing!! what other possibilities are there? could it make easy rom dumping? maybe even playing megadrive games on an emulator?

[Fonzie]

Seems interesting
In 15BPP, the 32x cannot show more than 320*192px screen Well, how do you do then for 448 height :P You used the 32x framebuffer in MASTER mode to merge both DRAM?

[Ash]

Since all the pics and vids are of the screen, why none that actually shows the genesis connected? For all we know that screen output is from..... a mac maybe?

[evildragon]

i have the Genesis VDP output an interlaced image, and the 32X is set to alternate even and odd lines (i could not possibly explain this any better, sorry), and it just works... (and i got a 224p output from the 32X easily-----i don't remember exactly how I programmed the 32X, as this part was actually completed a while ago.. i'd have to look at my code, to see what I did)

ash: I don't have a real Mac that is even capable of running OS 7, I wish though, im a Mac fan.. I talked to Joe about this actually.. i don't have any pics of the cartridge yet, since it's a prototype, and frankly, as a lot of ECO (Engineering Change Orders).. I'm only gonna take pictures of it when it's done (I will show a complete setup--dont worry)..

[evildragon]

Originally Posted by Ski_Dude_Andy

wow thats amazing!! what other possibilities are there? could it make easy rom dumping? maybe even playing megadrive games on an emulator?

ROM Dumpting: There's a cartridge in it already... Anyway, go to retrodev, you can ROM dump with a free SegaCD ISO image there

Emulator: That would be mad slow.. You wouldn't have real 2612 sound yet either, cause I can't get FM sounds working on OS 7..

[Melf]

This goes in the Sega Genesis forum.

[Fonzie]

Interesting man...
On genesis it would make 140KB of VRAM (and genesis only have 54KB max)
On 32x, it would make 560KB of VRAM (and 32x only have 256KB)...

I think you re-flashed the vdp's firmares to allow real time RLE decoding... clever dude.

[Genesis Knight]

Holy frickin' cow. Write a detailed article on this, now, or I will ban you.

And this has so many possibilites it's insane.

[16-bit pwnage]

That is awesome! I would never have thought a machine as old as the Genesis could be capable of something like this.

[Genesis Knight]

Well, remember - it's using the Sega CD and 32X as well.

[Joe Redifer]

Evildragon says he is going to try and implement one of the Sega CD PCM channels to do the sound since it can at least go up to 32Khz instead of 11050Hz. Not sure how he's progressing on that, but it might be tough. I'd also suggest using the Sega CD's 68000 as the main processor, but I don't think that thing can "have the floor" so to speak... it's always a slave to the Genesis.

Also, I tried to convince evildragon to get a SNES or N64 emulator working on it, but nothing like that exists for OS 7.

[TheGZeus]

You can access Sega CD Ram in 2mbit banks if you halt(right term?) the SCDs 68k.
However, that's not really an option if you want to use the PCM.

This has gottem me thinking in a completely different direction:
What about making a ram/peripheral interface cart for these systems?
If you increased the ram slightly and allowed the same hardware interfacing and eliminated the Mac part of the equation, you then have a simple 16/32 bit hybrid computer. There are enough Linux freaks out there for them to port it and some programs. Heck, do we even need to eliminate the boot ROM? Can it just be bypassed?
Leaving the 32x as a graphics card in that case would be moderately silly, but might be one of the better options in order to get max color depth/speed.

However, I honestly have severe doubts about the truth of this.
Reasons:
A. it's attached to an LCD screen. Does your screen have a SCART input? Most without can't accept 15khz horizontal ref. rate.
B. The resolution looks like 640 480. The 32X can't put out that high. The weird 'interlaced' mode you described doesn't make any sense at all. It could just be you describing it in a way I don't understand, but you can't 'backtrack' a scanline. You can draw ANOTHER line, but not until the next field. The Genesis does have an interlaced mode, but the 32x doesn't, to my knowledge( I could be wrong. Keep in mind, the 32x is a pass-thru in Genesis mode and so doesn't need to be compatible with everything the Genesis can do, and the interlace modes were rarely used).
C. I've never known a homebrewer to be shy about showing off their accomplishments in any form.
D. you associate with the above poster.

[Joe Redifer]

I'm sure evildragon can answer far better than I can, but here's my take:

A - He told me awhile ago that he had an LCD that could sync down to 15k.

B - If you're referring to the screenshots, I imagine that's just the way the Mac takes screenshots. Now if you did a frame grab from the analog video output, I'd bet it'd be much different as two quadrants of the screen can never be seen as far as I understand it.

C - ?

D - As of right now, I haven't seen more than anyone here. I just saw it sooner.

[Joe Redifer]

Oops, I didn't mean "two quadrants". Brain fart. But I did mean something similar, being as half of the pixels would never be seen at 60Hz.