Subject: RE: GameBoy Port
To: David Edwards <>
From: John A. Maier <>
List: netbsd-ports
Date: 02/28/2000 16:32:00
> The Gameboy has a bastardized (Z80 derivative) processor, a

You might as well stop there.  The Z80 is a 16 bit 64 Kilobyte maximum   
CPU.  I have hack on these guys back in the 80's more than I'd like to   

If you remember the Coleco Adam (the Coleco video game system made into a   
computer) there were some die-hards who made some 512K expansion cards   
that did some exotic bank switching.  In theory you could get up into the   
1Meg region this way, but it is slowwwww.

Looking at the schematic on the web page, it is the Z80A, which was a   
4Mhz version.  So if a port were possible, a VAX 750 could out perform   
you. Zilog did make some 8 10 and even 12Mhz version that are used in   
asics cores.

The Z800 is code compatible with the Z80 and can segment offset up to   
1Meg.  They latter beefed it up to access more memory, I know little   
about it.  Since it didn't have a protected mode, it out of the picture.

The Z8000 was Zilogs answer to the 286/386 but with Z80 looking registers   
and instruction, though they were machine code incompatible.  It was   
limited to 4Megs if memory servers me correctly with seperate code and   
data space so you could go up to 8Megs.  I think it actually had a   
protected mode of operation, so in theory...NetBSD for Z8000 sounds   

There is a Z80000 of which I know nothing about.

> If nothing else, porting to this platform would be a way cool
> hack, even
> cooler than hacking Linux to run on a Palm Pilot. I will

No it would be amazing!  the smallest kernel of 1.4x i386 I managed to   
create are around 600K.

> suggest that the
> lack of anything remotely resembling a MMU may cause some non-trivial
> problems in the porting process, but I'm certainly not going to say it
> can't be done. :) It may be a good idea to track down the UZI project,
> which was a UNIX-y OS targeted at the Z80. (It ended rather a
> lot of years
> ago, so you may have problems finding information.)

I remember reading about it, but I know nothing about it.  I remember   
reading about a multi-user unixish Z80 system around 1984, but it had no   
TCP and rather limited functionality.

Charles Moore, of Forth fame, had a multi-user Z80 based computer in the   
mid 80's that was rumored to be amazing.  Seems that it could   
functionally do most everything a PDP-11 could do with only 64K!

As for using the Gameboy as a robotics controller, you bet!  Those of us   
who remember the Sinclair ZX-80/ZX-81 and or Timex Sinclair, they were   
Z80 based.  2K on board latter 4K!  People used them in the same capacity   
all of the time.  Funny 20 years latter and people doing the same thing!

Basically, you should really think more about CPM...

Okay, I've reminisced enough, 31 is a frustrating age :-)