APPLE II GS

[danwinslow]

Ok, so, if I had me an Apple IIGS, could I (in theory) replace the OS rom with a modified atari OS? I realize that not having antic, pokey, etc might be a slight issue ( :rolleyes: ), but I was wondering if it could in theory be done. Mostly wondering about burning new ROM chips, etc.

Edited March 11, 2010 by danwinslow

[tribe7]

I think you might be able to make it an ST not so easily(lol)

[Rybags]

In theory, yes.

 

No idea though if the IIgs even has a text mode. I guess if it's bitmap only, it could be "emulated".

 

Substantial changes/additions to the OS would be needed... so the 10K OS from the 800 would probably bloat out beyond 16K. Stuff like disk I/O primitives and the keyboard scan would need discrete coding, then you'd need to translate the codes to A8 ones. Biggest hurdle might well be the screen. Even if PMGs aren't emulated, the entire screen would still need to be converted to something the IIgs could display.

 

Bottom line though - you'd end up with in essense an emulator. One that wasn't particularly compatible, would probably run very few ML games, and in all likelihood would be somewhat slower than a real Atari.

[danwinslow]

In theory, yes.

 

No idea though if the IIgs even has a text mode. I guess if it's bitmap only, it could be "emulated".

 

Substantial changes/additions to the OS would be needed... so the 10K OS from the 800 would probably bloat out beyond 16K. Stuff like disk I/O primitives and the keyboard scan would need discrete coding, then you'd need to translate the codes to A8 ones. Biggest hurdle might well be the screen. Even if PMGs aren't emulated, the entire screen would still need to be converted to something the IIgs could display.

 

Bottom line though - you'd end up with in essense an emulator. One that wasn't particularly compatible, would probably run very few ML games, and in all likelihood would be somewhat slower than a real Atari.

 

Yes, that mostly what I was thinking. Probably could do a straight up emulation over the GS OS, but of course that'd be quite slow. I was thinking that maybe an OS replacement would be faster, but as you point out theres so much emulation left over it's probably a wash.

[atariksi]

In theory, yes.

 

No idea though if the IIgs even has a text mode. I guess if it's bitmap only, it could be "emulated".

 

Substantial changes/additions to the OS would be needed... so the 10K OS from the 800 would probably bloat out beyond 16K. Stuff like disk I/O primitives and the keyboard scan would need discrete coding, then you'd need to translate the codes to A8 ones. Biggest hurdle might well be the screen. Even if PMGs aren't emulated, the entire screen would still need to be converted to something the IIgs could display.

 

Bottom line though - you'd end up with in essense an emulator. One that wasn't particularly compatible, would probably run very few ML games, and in all likelihood would be somewhat slower than a real Atari.

 

Yes, that mostly what I was thinking. Probably could do a straight up emulation over the GS OS, but of course that'd be quite slow. I was thinking that maybe an OS replacement would be faster, but as you point out theres so much emulation left over it's probably a wash.

 

IIGS is supposed to be backward compatible with the IIe and that has text modes so perhaps it can run the BASIC programs with the replaced OS as long as you somehow suppress/remap Atari-specific hardware I/O.

[JamesD]

The IIgs had all the old graphics and text modes of the Apple II series as well as the new graphics.

But what you propose still wouldn't be very feasible.

 

You could build an Atari on an Apple II card kinda like its CP/M & 6809 cards or like the Amiga bridge board.

But then you have to boot the Apple, run a program to boot the Atari and set the IIgs as a slave.

Then the Atari has to send info to the IIgs to do anything on the 65816 and new graphics.

And the 65816 has to send info to the Atari card to use any old hardware.

Very ugly because you can't just hang the old hardware off off the IIgs at the same address, there's buss timing issues, etc...

 

<edit>

BTW, the Apple II series uses a weird memory layout for the screen for all old text and graphics modes. It was a hack to use slower chips. That would even make text only screen emulation slow.

Edited March 11, 2010 by JamesD

[frogstar_robot]

 

 

You could build an Atari on an Apple II card kinda like its CP/M & 6809 cards or like the Amiga bridge board.

But then you have to boot the Apple, run a program to boot the Atari and set the IIgs as a slave.

Then the Atari has to send info to the IIgs to do anything on the 65816 and new graphics.

And the 65816 has to send info to the Atari card to use any old hardware.

Very ugly because you can't just hang the old hardware off off the IIgs at the same address, there's buss timing issues, etc...

 

 

Rather than make a card that boots the entire A8 system, a card that merely makes the A8 chipset accessible may be more feasible. Basically, just map the chips into areas that don't conflict with existing hardware then rewrite one of the Atari OSes that have already been ported to the 65816 to use it. To further ease this hackery, mix the video output with the IIGS output rather than replace it. Now as to why, I dunno. It would be as compatible with a regular A8 as a 5200 is.

[R.Cade]

Yeah, sure, just swap out the ROM chips and I'm sure it'll work fine.

 

 

Uh, no. That's pretty much like trying to exchange brains in some living creature. You can probably get the parts to fit, but no way will either one work after that.

[LoTonah]

I'm still wondering who is going to design a 130XE with 1Mb memory/VBXE/AMY/1090XL in a GS form factor.

[atariksi]

Yeah, sure, just swap out the ROM chips and I'm sure it'll work fine.

 

 

Uh, no. That's pretty much like trying to exchange brains in some living creature. You can probably get the parts to fit, but no way will either one work after that.

 

Well, some parts are just algorithms based on 6502 instructions and memory. The Atari 400/800 FPU ROM from $D800..$DFFF would probably work just fine without any modifications. And once the rest of the OS is patched to remap/suppress the hardware related I/O, BASIC should boot up since it doesn't do direct hardware I/O but goes through the OS.

 

If you have a souped up Atari, it should be easier to go the other way (run Apple ROM on Atari).

[Tom-Lynx]

I think it would be much easier to gut an Apple IIGS case and install an Atari computer motherboard, even if you have to do lots of cutting.

[jaybird3rd]

Here's a related question: can the 65816 from the ][GS be used as a CPU upgrade for an Atari XE? Or is this chip not pin-compatible with Sally?

[Bryan]

Here's a related question: can the 65816 from the ][GS be used as a CPU upgrade for an Atari XE? Or is this chip not pin-compatible with Sally?

 

Sure and it's already been done. You need to build an upgrade that puts the Atari system on the bus for accesses in the first 64K and make it use a local bus (RAM/ROM/whatever) above that. If you want to get really slick you make it run faster from local RAM.

 

EDIT: and no, it's not pin compatible, although there is a version that works in the place of a standard 6502.

Edited March 11, 2010 by Bryan

[JamesD]

Ok... a couple things here. You can swap out the IIgs ROMs for RAM just by configuring the existing hardware bank switching to do it. That means you could potentially load the Atari ROMs in RAM and run it from there.

If you patched the ROMs you could probably hack them to let some text programs run... beyond that requires the Atari hardware.

 

But, putting the Atari hardware on an Apple II card doesn't mean that it can be addressed at the same location as on the Atari. It seems to me there is some switching going on as far as card slots go and the cards can only use certain addresses. The Atari chips would have to be addressed at a location the Apple II cards can support and NOT use addresses always reserved for the Apple II motherboard... things like RAM/ROM banking. That alone tells me it's not possible with a regular Apple II card. At best you can add a POKEY sound chip to the IIgs so you could play Atari songs.

 

To make matters worse the Atari hardware still doesn't have access to the IIgs memory. I suppose it could use DMA but it would be really ugly if not impossible. The Apple II buss runs at a different speed than the Atari buss. The IIgs still has to run slots at a slow speed (slower than Atari) for backwards compatibility, and *if* they can be run fast... then it's faster than the Atari buss. Ultimately, the Atari hardware has to have it's own RAM... RAM which the IIgs could access at a different speed which means dual port RAM. And then the IIgs has to bank to the memory address because the card slots don't let the IIgs see all the RAM at once. If you have to do that... you can't run existing software. Put a separate CPU on the card and you have a bridge card similar to what the Amiga had.

 

I did think of one *potential* way around the last issue. The Atari board would have to plug into the RAM expansion port of the IIgs. Then you could access all the Atari RAM without banking. However, that card slot doesn't use the first 64K... that RAM is on the motherboard. *IF* the 65816 could be configured to think it was executing things like it were in the fist 64K you might be able to do it. However, the stack *MUST* be in the first 64K on the 65816, so the stack would lie outside of Atari RAM and the Atari hardware couldn't access it... which is possible on the Atari if what other people have posted is true. So you have partial compatibility. And before you even think of saying YAY... I believe the 65816's 6502 compatibility mode requires you use the first 64K. I don't know enough about the 65816 to know if it could run the Atari 6502 code from anywhere in memory and even if it can... if the CPU isn't in compatible mode it may still break software. I've just started playing with the 65816 so I don't know. And then there is still the speed difference between the IIgs buss and Atari hardware ports. It's an asynchronous mess.

[sloopy]

Here's a related question: can the 65816 from the ][GS be used as a CPU upgrade for an Atari XE? Or is this chip not pin-compatible with Sally?

 

i have a 65816 cpu from a IIgs in my 130XE, with draco030's os in it... runs fine, albeit at stock speed... there is a pic of it here on the forums, from when it was in my 800XL... if you want to build one yourself to play with let me know...

 

sloopy.

[atariksi]

Here's a related question: can the 65816 from the ][GS be used as a CPU upgrade for an Atari XE? Or is this chip not pin-compatible with Sally?

 

i have a 65816 cpu from a IIgs in my 130XE, with draco030's os in it... runs fine, albeit at stock speed... there is a pic of it here on the forums, from when it was in my 800XL... if you want to build one yourself to play with let me know...

 

sloopy.

 

Where's the picture and schematic for 800XL? It would still count as accelerator since you can do 16-bit reads/writes in less time than 6502C. I guess you need some logic to implement the HALT line so can't just pop it in to replace the 6502C. Shouldn't it run normal Atari OS if it boots up in emulation mode?