Re: [hatari-devel] add support for TT ram ?

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Le 10/12/2014 00:59, Nicolas Pomarède a écrit :

By the way, I wonder if TOS 4.04 will detect this extra RAM.

Under TT, extra RAM is at 0x01000000, but as the falcon was designed to
have only 24 bits of address, I don't know if TOS 4.04 includes the
necessary code from TT's TOS to check this RAM.

Did someone already test this ? Maybe a patch will be needed for TOS 4.04.

I had a look at boot sequence for tos 3.06 (TT) and 4.04 (Falcon).

On TT, detection code will read/write values at address $1020000 and more, until it reaches a bus error. In that case, last address without a bus error will mark the end of the TT ram space.
Start address is always set to $1000000.

This means that if there's no TT RAM, addresses at $1000000 - $1400000 should give bus errors.

End address for TT ram will be written to $5A4, else 0.l is written if no TT ram at all.
$1357bd13 is written at $5A8 to validate the value in $5A4.

After that, TOS does a second memory test, that's the one were a black bar is going down from right to left. This test uses the values in $5A8 and doesn't rely on bus error or specific HW accesses anymore.


On Falcon, there no detection code to scan at addresses $1020000 and more. This is normal, because the 68030 in the falcon can only address 24 bits. But latter, when doing the 2nd memory test (with the black horizontal bar), TOS will use the value at $5A4 to check for extra RAM. So, a patch at address $5A4/$5A8 might work and we could have more RAM in the Falcon.

This part needs to be checked, at least the code is present in TOS 4.04, but I need to ensure it's really used.


Nicolas



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