Re: C128 memory - B series compatibility - Basic using 256k - a new version of the hardware for 256k

From: smf <smf_at_null.net>
Date: Tue, 8 May 2018 08:59:57 +0000
Message-ID: <c564de86-a5c2-f2c1-3f7c-104249fc88a6@null.net>
On 08/05/2018 01:18, Jim Brain wrote:

>
> I'd recommend using 4kB pages, using one $d50x register to hold the 
> "task" number, and using 16 of the free registers to hold 16 "page" 
> registers, 1 for each 4kB page  At 8bits, that'd be able to manage 
> 1MB, while extending the MMU regs to 13 bits would allow 32MB of 
> mapping.  With a task register, you could have 256 mappings.  The 
> additional 3 bits could be used for "IRQ on write, mark RAM as 
> read-only, and reserved.
>
The C128 was designed so you can configure all your banks and then 
switch between them with $ff0x accesses, without having to page the 
$d50x registers back in. Therefore I think you should consider adding a 
task register into the $ff0x range.

I believe ram/rom shows through in $ff0x except where the existing 
registers are defined, so to remain backward compatible you'll need to 
enable it with a magic sequence in the $d50x range first.
Received on 2018-05-08 11:00:02

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