(more) RAM under the OS

[DamageX]

I am wondering if anyone has ever rigged an A8 to have more banks of RAM or ROM in the $C000-$FFFF area. I'm dreaming of one OS/DOS that "does it all" like having harddisk support, hi-speed SIO, etc. at the same time, and having compatibilty with as many programs as possible, even ones that need a low MEMLO and RAM under the OS.

 

At least with an extra bank of RAM there you could boot a "soft-OS" like MyIDE and still be able to run programs that need 64K. And it seems like this would take only a small amount of work (certainly compared to rewriting DOS). Has it been done already?

[drac030]

I am wondering if anyone has ever rigged an A8 to have more banks of RAM or ROM in the $C000-$FFFF area. I'm dreaming of one OS/DOS that "does it all" like having harddisk support, hi-speed SIO, etc. at the same time, and having compatibilty with as many programs as possible, even ones that need a low MEMLO and RAM under the OS.

 

At least with an extra bank of RAM there you could boot a "soft-OS" like MyIDE and still be able to run programs that need 64K. And it seems like this would take only a small amount of work (certainly compared to rewriting DOS). Has it been done already?

 

No, somethis else has been done: in order to keep the MEMLO low and have highspeed SIO and harddisk support, the bulk of DOS code was put into one of additional 130XE banks at $4000-$7FFF. This is called SpartaDOS X.

[+warerat]

I am wondering if anyone has ever rigged an A8 to have more banks of RAM or ROM in the $C000-$FFFF area. I'm dreaming of one OS/DOS that "does it all" like having harddisk support, hi-speed SIO, etc. at the same time, and having compatibilty with as many programs as possible, even ones that need a low MEMLO and RAM under the OS.

 

At least with an extra bank of RAM there you could boot a "soft-OS" like MyIDE and still be able to run programs that need 64K. And it seems like this would take only a small amount of work (certainly compared to rewriting DOS). Has it been done already?

1029784[/snapback]

 

Technically, yes. In use, no. My 800 to XL mod uses a 32K SRAM for the RAM under the OS, but I ground A14 to use only 14K of the chip (remember $D000-$D7FF can never be mapped out). One could technically wire a switch to it and have two 14K RAM OS's. But no compatible way to control it from software, unless someone decided "from here on out address $XXXX will control the OS banks).

 

I know $D1XX is used by PBI, I'd like to see a comprehensive list of devices that map $D5XX, $D6XX, and $D7XX so any new devices won't bump into each other and that way we can design around everyone else's memory maps.

 

For example, I'd like to see that new video board with the 512K mapped into the GTIA space assuming all the registers can fit.

Edited March 8, 2006 by warerat

[mos6507]

I think the best alternate location for banked memory is the cart address-range. It's already set up for that, it's just that people think of carts as only good for ROM, not RAM.

 

Also, with a 2nd PIA chip you can have a lot more banks than you could otherwise (at least not without sacrificing XE compatibility).

[DamageX]

No, somethis else has been done: in order to keep the MEMLO low and have highspeed SIO and harddisk support, the bulk of DOS code was put into one of additional 130XE banks at $4000-$7FFF. This is called SpartaDOS X.

Heh, I didn't know that! I've never used SDX, and for some reason I thought it was a cartridge... I've only ever had an 800XL though anyways, with just 64KB. Someday I'll have to upgrade I guess...

I think the best alternate location for banked memory is the cart address-range. It's already set up for that, it's just that people think of carts as only good for ROM, not RAM.

Well, at least there wouldn't be the 2K hole for I/O ports but is there any advantage to using the cartridge area instead of the 130XE extended memory area?

Also, with a 2nd PIA chip you can have a lot more banks than you could otherwise (at least not without sacrificing XE compatibility).

Yes I was also thinking about a 2nd PIA, it could be mapped somewhere in $D3xx so as not to "bump into" other devices like warerat was saying.

[drac030]

Heh, I didn't know that! I've never used SDX, and for some reason I thought it was a cartridge...

 

It is a cartridge, the SDX loads from it into memory, and also partially resides on the ROM too. The main part of the DOS, i.e. the high speed SIO driver and the filesystem driver loads into RAM. DOS buffers also reside there. Depending on the configuration (and availability) it may be the main RAM (MEMLO goes very high then, however), the RAM under the ROM or the bank-select RAM at $4000.

Edited March 9, 2006 by drac030