Breaking the 2MB Chip RAM limit

[Thorham]

Originally Posted by ptyerman

Scanners for one on the Amiga are almost useless because of the lack of chipram.

Not when you scan to fastmem and use image processing software that copies data from fastmem to chipmem. Adpro is a good example of this. Brilliance is another. With these programs you can use humongous images and never run out of chipmem.

[majsta]

@mc6809e that is very interesting approach you said. It could be tricky but it can be done. I didn't think about this approach. Smart if I may say

[Cymru]

Rewriting apps to make use of your "new chip ram" makes less sense than using RTG graphics and audio.

The on MB chip system was a huge advantage in 1985 when CGA/EGA and audio beeps were PC heaven, but less so later.

[hooverphonique]

Originally Posted by mc6809e

It might be possible to use a bank switching type system added on to the chipset.

I believe all register accesses are visible on the chip register address bus (RGA). It might be possible to determine what DMA is occurring and bank switch based on this information. Each DMA channel would then have it's own 2MB space.

A clever design might let the CPU access a bank as fast ram when no other DMA was going on in that bank.

that might be doable, but that requires modifying the OS as well, then..

[Cymru]

Also, bank-switching is a bit dodgy.

[desiv]

Originally Posted by Cymru

Rewriting apps to make use of your "new chip ram" makes less sense than using RTG graphics and audio. .

That was one of the nice things about the FPGA Arcade extra CHIP demo.
They were able to use a piece of software to display a much larger picture without (from my understanding) having to modify the software.

The software asked for XX memory, and the OS, seeing it had more, gave it to the app.

If that isn't uncommon for memory allocation, then it's possible not a lot of apps would need to be modified...

desiv

[pandy71]

IMHO when CHIP cycle can be hidden there is no need to do banking - DMA can be used to transfer memory content between 2MB and remain part of memory - also shadow/window can be used to extend beyond 2MB (this one can be dynamic ie each pointer can receive own up to 2MB window).


But this is really unecessary complication - new HW should provide basic compatibility with legacy software - video can be overlay/combined with new video, old audio with old audio etc.
Old chipset can be tweaked, new bits and register can be added - there is few gaps but still - old limitations are to big.

[Amicol]

After struggling like hell for a while to minimise chip memory usage in Workbench, I got thinking about how an increase would allow the use of higher resolutions without worrying about free chip memory.

I obviously know the limit is 2mb on a Real Amiga (same isn't true for emulation or fpga). So what chip is limiting the Chip RAM?
And if this is the only thing imposing the limit, would a replacement (maybe fpga replacement/add-on) be possible to increase/or remove the limit?

If so, I'm sure there would be a market for such a product....

[jbenam]

IIRC it's an inherent limitation in the Alice chip. I presume that to have more than 8MB it would require an entire Alice redesign without the limit in place.

Who knows, maybe one day... with either an FPGA or Jens' fabled Clone-A project...

[TCD]

Threads merged.

[SpeedGeek]

Originally Posted by Amicol

After struggling like hell for a while to minimise chip memory usage in Workbench, I got thinking about how an increase would allow the use of higher resolutions without worrying about free chip memory.

I obviously know the limit is 2mb on a Real Amiga (same isn't true for emulation or fpga). So what chip is limiting the Chip RAM?
And if this is the only thing imposing the limit, would a replacement (maybe fpga replacement/add-on) be possible to increase/or remove the limit?

If so, I'm sure there would be a market for such a product....

Did you try Fblit? Alice and Fat Agnus limit Chip Ram to 2MB max. Some versions of Fat Agnus only give 512K/1MB of Chip RAM.

But the Amiga memory map also limits it to 2MB. So even with new FPGA versions (or a bank select hack) extra Chip RAM will still be kludged into the Amiga memory map.