32-bit chip memory

[digitalMedic]

Hi all,

Happy Holidays! Hope everyone had a great Christmas.

I was trying to use SysInfo with WinUAE and kept getting GURU meditation errors. I turned off 32-bit Chip memory and SysInfo worked. This was the second time that 32-bit Chip memory caused an issue. What is 32-bit Chip memory and how come it causes problems?

Rick

[Rotareneg]

It's an emulator hack that lets you enable far more chip ram than a real Amiga could actually have. Can be handy if a program is system-friendly enough to not freak out because it expected to never see more than 2 MB and you want to work on huge images and aren't using RTG.

[Toni Wilen]

Probably some kind of buffer overflow somewhere in sysinfo because it crashes if >64M. (Always start with small value!)

[digitalMedic]

Ah, ok. Got it. Is the original chip memory 32 bit?

[AmigaHope]

Originally Posted by digitalMedic

Ah, ok. Got it. Is the original chip memory 32 bit?

In this case, "32-bit" means the address length. The custom chipset on all Amigas from OCS all the way to AGA only ever worked on a 24-bit address bus, and even then it was only the gate arrays -- the DMA controllers were only really addressing 512k (OCS) to 2M (Highest ECS, AGA) of chip memory. Even the most forward-thinking software of the time only really expected 24-bit addressing in the chipset (since were early provisions for a later 8M Super Alice that never came). When you set that option, *this* is what you are messing with. It's not suprising that some software crashes.

In other cases you might hear about 32-bit chip memory in terms of DATA bus width. On some ECS (A3000 series) and on all AGA machines, chip memory is 32-bit accessible to the CPU, and on AGA Lisa also got 32-bit access to chip memory. This only affects bandwidth though, not addressing, and is not what this emulation option is talking about.

[digitalMedic]

Thanks! Great explanation.

[Toni Wilen]

It is called "32-bit" because "original" UAE chip RAM extension uses Z2 space (=max 8M) which is usually more than enough.

"32-bit chip" only exists only because it can!