As much memory as possible

[Samoteph]

Hello Atari devs!

I'm developing a game for Atari 520 ST and I need as much memory as possible.
The game uses GemDos to access files.
When the game start it is not mandatory for me to return to the desktop.

On Atari ST, The RAM seems to start at $5B4 but a part of this memory is used by TOS (end of TOS RAM at $4FA).
I've heard that some developpers copy their code in $5B4 to save memory. But how to stop TOS to use this part of memory?
Is it possible to use GemDos in this condition?

[mikro]

I'm not an expert in this area but I'd say you have to choose one: compatibility or purging the OS. :)

There is a few open source projects which offer an OS-independent way of managing files, assets, memory etc. Amiga Demo 2 by Leonard comes into my mind: http://leonard.oxg.free.fr/download/Ami ... ersion.zip.

The user space is from $5000 to $80000 for 512Kb machine

So that gives you about 492 KB of RAM (out of 512, not bad!).

Loading files seems to be pretty straighforward:

Code: Select all

	lea		$5000.w,a0		; user space to load the file
	moveq	#2,d0
	jsr		$1000.w			; $1000 is Kernel adress
	jmp		$5000.w			; jump in the file

It should be fairly easy to replace the demo with your game and use the underlying manager for loading files.

[sporniket]

https://freemint.github.io/tos.hyp/en/t ... ctors.html

Bus errors arise when one attempts to access regions of memory to which access is not permitted. In supervisor mode this really can be only nonexistent memory areas. In user mode this can also happen in attempting to access hardware registers or regions below $800.

[Eero Tamminen]

Some instructive reading on how not to do things: https://raw.githubusercontent.com/emuto ... atible.txt

[Samoteph]

Thank you for this information. Finally, I use a packer and a compression algorithm to minimize my memory footprint while respecting the OS

[elliot]

Does your game actually use GEM? Can you open files with TOS? I am not sure but I think you may have a little more memory if your game boots from disk (auto folder) before GEM loads. I may be wrong about this. Well it is def true if the user has ACCs and other "on boot" apps.

4Mb is a easy max memory you will get. You can also have "fast RAM" or "TT RAM" but I have no idea how one uses that. Is it STE or F?

[ThorstenOtto]

On Atari ST, The RAM seems to start at $5B4 but a part of this memory is used by TOS (end of TOS RAM at $4FA).

Don't know where you got those values from, but TOS uses much more memory. In TOS 1.04 for example usable memory starts at $A84E. The _membot system variable tells you the exact address.

It should be fairly easy to replace the demo with your game and use the underlying manager for loading files.

I would say that this doesn't save memory at all. You would then maybe be able to start at a lower address, at the cost of additional code for the filesystem routines instead of using GEMDOS. GEMDOS of tos 1.4 takes about 24k of code.

[metalages]

I have made the choice to get rid of the os and loads at $1000. The framework is a mix of asm and c without any standard lib. There is a tool to generate a floppy image with a resource management easy to use from the application. When loading from hd the application needs more memory. It preloads the disk image into additional memory and then the framework transparently copy from memory instead of loading at each load request. I don't think the loading code implementation takes more than 24kb as the whole demo code fits in less than 100kb (code + statics) and everything runs in 1mb.

https://github.com/jhubrt/demOS