My special computer is a Sega TeraDrive. A 286 system co-developed by IBM
and Sega. It's a 10MHz 286 based on the IBM PS/1 2011, but with a complete Sega MegaDrive on the motherboard. Unlike the Amstrad Mega-PC, the two systems are linked through a bus arbitrator.

After setting some registers and doing some port writes, you can access the 68000's memory space from the PC (including accessing the sound chips, VDP and controller ports), and likewise, you can access the PC's memory and IO space from the MegaDrive (including the VGA chip and any devices on the ISA bus).

I wrote a demo showcasing these abilities last year: https://www.youtube.com/watch?v=yjg3gmTo4WA

I wasn't real sure what I was watching at times, but it seemed really neat!
Does the process require two monitors?


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My special computer is a Sega TeraDrive. A 286 system co-developed by IB and Sega. It's a 10MHz 286 based on the IBM PS/1 2011, but with a comple Sega MegaDrive on the motherboard. Unlike the Amstrad Mega-PC, the two systems are linked through a bus arbitrator.

I never knew this existed! What a cool and unlikely partnership...
So with this, what of the IBM can be accessed by the Sega and visaversa?
I see you can get Sega sound on the PC side - can that be accessed by
virtually anything that supports a sound card?

I'll need to watch the video sometime... Tomorrow maybe!

|14Dave!
|05(|13dflorey|05)
|13Retro16 BBS |05--> |14bbs.retro16.com |05(|13WIP|05)
|07No one expects the Spanish inquisition!

--- Mystic BBS v1.12 A46 2020/08/26 (Windows/32)
* Origin: Retro16 BBS (21:1/226)

I wasn't real sure what I was watching at times, but it seemed really neat! Does the process require two monitors?

Having two monitors is mostly for swag, there is a register you can set to determine which video chip is connected to the VGA port on the back of the system, the PC's VGA chip, or the Mega Drive VDP.

The integration between the two sides was essentially undocumented until
quite recently. A few owners including myself are trying to create the documentation based on experimentation and reverse engineering. We have it pretty well covered now, but there are still secrets lurking within!

Such as running the two CPU's simultaneously!
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I never knew this existed! What a cool and unlikely partnership...
So with this, what of the IBM can be accessed by the Sega and visaversa?
I see you can get Sega sound on the PC side - can that be accessed by virtually anything that supports a sound card?

From the PC side, you can access on the MD side:
- All RAM
- All VDP registers (incl VRAM and CRAM)
- Yamaha OPN FM chip
- Ti PSG chip
- Z80 memory and registers
- Joystick ports

You cannot access the cartridge slot or the TMSS (lockout chip) ROM.

From the MD side, you can access on the PC side:
- All RAM
- All ROMs (e.g. system BIOS, VGA BIOS, and any option ROMs)
- All IO space (e.g. serial/parallel ports, VGA registers, interval timer, any ISA cards not requiring DMA or interrupts like AdLib or POST analyser cards)

You cannot use BIOS routines, as the CPU is halted, so no DMA or anything that relies on interrupts.

I'll need to watch the video sometime... Tomorrow maybe!

Let me know how you go!

As of right now, there are exactly *TWO* packages that make use of the TeraDrive's capabilities. Puzzle Construction Set, a demo included with the system showing off what can be done. And "The Manhole", an adventure game by Cyan (of MYST fame), published by Activision, which uses a special driver to access the Yamaha OPN FM chip.

And I guess my demo makes three! :D

Unfortunately there is a specific setup routine needed to unlock the MD hardware from the PC side, and bespoke ways of accessing it, so you can't use any old game with, say, AdLib support.

Hope this answers your questions!

Cheers
--- Ezycom V2.15g0 01FD0295
* Origin: >> Pool's Open - The RetroSwim BBS (21:2/121)

From the PC side, you can access on the MD side:
- All RAM
- All VDP registers (incl VRAM and CRAM)
- Yamaha OPN FM chip
- Ti PSG chip
- Z80 memory and registers
- Joystick ports

You cannot access the cartridge slot or the TMSS (lockout chip) ROM.

From the MD side, you can access on the PC side:
- All RAM
- All ROMs (e.g. system BIOS, VGA BIOS, and any option ROMs)
- All IO space (e.g. serial/parallel ports, VGA registers, interval
timer, any ISA cards not requiring DMA or interrupts like AdLib or POST analyser cards)

You cannot use BIOS routines, as the CPU is halted, so no DMA or
anything that relies on interrupts.

I'll need to watch the video sometime... Tomorrow maybe!

Let me know how you go!

As of right now, there are exactly *TWO* packages that make use of the TeraDrive's capabilities. Puzzle Construction Set, a demo included with the system showing off what can be done. And "The Manhole", an adventure game by Cyan (of MYST fame), published by Activision, which uses a
special driver to access the Yamaha OPN FM chip.

And I guess my demo makes three! :D

Unfortunately there is a specific setup routine needed to unlock the MD hardware from the PC side, and bespoke ways of accessing it, so you
can't use any old game with, say, AdLib support.

Hope this answers your questions!

That is really cool. I guess it makes sense that the PC CPU is halted - I did wonder about that. Was such an experimental time...

|14Dave!
|05(|13dflorey|05)
|13Retro16 BBS |05--> |14bbs.retro16.com |05(|13WIP|05)
|07No one expects the Spanish inquisition!

--- Mystic BBS v1.12 A46 2020/08/26 (Windows/32)
* Origin: Retro16 BBS (21:1/226)