Re: MMU questions?

["Jesús Cea Avión" <jcea@argo.es>]

> Can the MMu work in both ways, Memory protection ON AND virtual
> memory?

Yes. You can DO Protection and Virtual memory. In fact, internally
virtual memory (if you page to disk) is implemented using memory
protection.

> If so, why can't outside work with memory protection?

Since both features are not independent, in general you need a program
which can manage both. Obviously Outside can´t. It had been programmed
to care only about VM.

You could implement a layering strategy to split Virtual Memory and
Protection, but nowadays no such scheme exists in the Atari World. MACH
architecture in this topic is nice, for example. We need to design a
standard.

> 2) Is the Vmem (on Falcon for example or TT without TTram) seen as
> TTram? or ALT RAM?

I don't know differences between TTRAM and Alt RAM. In general, Virtual
Memory can only be accessed using the CPU, whom knows about paging and
MMU. Devices don´t know. So you can´t use virtual memory for DMA audio
playing/Hard Disk or Video Memory for the Videl. AFAIK, ALT/TT Ram
distintion is to allow the system to know about memory that can´t
allocate for such things.

> like, is it possible to have a TT with 4 of STram, 8 meg of TTram and
> 10 meg of vmem?

Virtual memory maps to TTRAM/Alt Ram. You can have 8MB of Alt RAM, real
ram, used to "buffer" 32MB of Virtual Ram. The current used pages are
"cached" in Alt RAM. The Least recent used pages are paged to disk and
only reloaded when a program references the page. That's the VM working
model.

> 3) what is the correct pointer containing the MAX TTRAM (physical)?
> and MAX Vmem?

I couldn´t tell...

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