Limitations in current 32X emulators

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Chilly Willy
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Joined: Fri Aug 17, 2007 9:33 pm

Limitations in current 32X emulators

Postby Chilly Willy » Thu Feb 23, 2012 7:22 am

I was working on adding cd mode 1 music to my 32X stuff and ran into a limitation of current emulators - no one emulates mode 1 AND 32X at the same time. My mode 1 demo for MD works fine with Fusion, but my mode 1 for 32X does not. It works fine on real hardware. This is a case where I needed real hardware to figure out what was going on. :lol:

Anywho, mode 1 + 32X is actually rather simple - it's just like mode 1 + MD. The cd still shows at 0x400000 to 0x7FFFFF. You DO NOT need to set RV to access the cd from the 68000 while running 32X code; in fact, setting RV interferes with the CD space, preventing it from working right. So the 68000 address space with 32X + CD looks like this:

0x000000 to 0x3FFFFF = 32X BIOS space
0x400000 to 0x7FFFFF = CD space
0x800000 to 0x87FFFF = frame buffer
0x880000 to 0x8FFFFF = fixed rom space
0x900000 to 0x9FFFFF = banked rom space
0xA00000 to 0xDFFFFF = IO
0xE00000 to 0xFFFFFF = work ram

0x000000 to 0x3FFFFF = rom space
0x400000 to 0x7FFFFF =
0x800000 to 0x87FFFF = frame buffer
0x880000 to 0x8FFFFF =
0x900000 to 0x9FFFFF =
0xA00000 to 0xDFFFFF = IO
0xE00000 to 0xFFFFFF = work ram

You can read the CD BIOS from 0x400000 with RV set, but you cannot write the program ram. I imagine you can't write the word ram either, but I haven't tried it. Attempting to write the program ram with RV set locks the 68000 solid - you can't even reset at that point... you have to power off the console. With RV clear, the CD operates just like normal.

I'll be posting a version of Wolf32X with CD audio sometime tomorrow so people with flash cards can try it. This is a backport of the CD audio that is part of my update to Wolf3D. I haven't finished that yet, so I figured I could put it in the existing version for folks who like music. I certainly like it better with music. :D

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