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Old 27 December 2019, 17:43   #1
digitalMedic
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32-bit chip memory

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
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Old 27 December 2019, 17:54   #2
Rotareneg
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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.
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Old 27 December 2019, 17:55   #3
Toni Wilen
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Probably some kind of buffer overflow somewhere in sysinfo because it crashes if >64M. (Always start with small value!)
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Old 28 December 2019, 06:17   #4
digitalMedic
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Ah, ok. Got it. Is the original chip memory 32 bit?
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Old 28 December 2019, 06:37   #5
AmigaHope
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Quote:
Originally Posted by digitalMedic View Post
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.

Last edited by AmigaHope; 28 December 2019 at 06:42.
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Old 28 December 2019, 12:42   #6
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Thanks! Great explanation.
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Old 28 December 2019, 12:49   #7
Toni Wilen
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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!
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