Date   : Fri, 18 Mar 2011 08:45:33 +0100
From   : kortink@... (John Kortink)
Subject: How much sideways ROM is possible ?

On Fri, 18 Mar 2011 07:22:33 +0000, Rob <robert@...> wrote:

>On 18 March 2011 02:03, David Hunt <dm.hunt@...> wrote:
>
>[...]
>
>> A bit of a long shot, but can the OS use all 8 bits of the value of ROMSEL
>> or would the OS need patching, that would give you 256 ROMs (4M bytes!) :)
>
>Quick answer: No.  Far too many things rely on that number being <16,
>lots of 16 to 0 counts, and there are various tables that are only 16
>bytes in length that are indexed by ROM number that you would have
>trouble extending.   Not to mention having to do the same again for
>every ROM you want to include.

Most ROMs don't rely on the '16', or even use the ROM number
passed to them. If they do, it's true that there can be various
complications. But only the OS accesses the array at 0x2A1, so
that can be fixed, and ROMs using the one at 0xDF0 (in relation
to workspace or other purposes) could exist unpatched in one of
the first 16 slots (or be patched, although it could get messy).


John Kortink

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