Re: [hatari-devel] About RAM size comments (commit 6c827e5)

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On 1/2/21 6:13 PM, Christian Zietz wrote:
Eero Tamminen schrieb:
Then why is the MegaSTE mentioned in the comments for 8 MB and 10 MB?

Why MegaSTE wouldn't support 8MB, when max is 10MB?

One has to distinguish between two things:

- All machines with "ST" in their name (ST, MegaST, STE, MegaSTE) are
limited to 4 MB of ST-RAM because of their MCU design.

Thanks, I didn't know that about the Mega* machines!

- If you design a new MCU IC, you can fill the entire unused address
space with ST-RAM, which means 10 MB on the MegaSTE (because VME starts
at $A00000), 14 MB on the STE, 14 - 15 MB on the ST/MegaST (depending on
whether you want to support TOS 2 ROMs).

So, yes, with a newly designed MCU, the MegaSTE would support 8 MB. But
so would the ST, MegaSTE, and STE. Hence, why does the comment for 8 MB
specifically mention the MegaSTE, when it is no different from the other
STs in that regard?

So the limits are actually:

- ST/MegaST/STE/MegaSTE (unmodified)

10MB, due to VME: [1]
- TT
- MegaSTE with HW mods

- Falcon
- ST/MegaST/STE with HW mods

What about 6MB, is that actually a legal ST-RAM
amount?  On all the machines?

Btw. Has somebody actually done the TOS 2 ROM
15MB ST/MegaST HW setup?

[1] Because Hatari doesn't support VME, and allows
access to VME register area, currently one can
actually specify *and* use 14MB also on MegaSTE
and TT.

	- Eero

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