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

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

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:

4MB:
- ST/MegaST/STE/MegaSTE (unmodified)

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

14MB:
- 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