[LMH]SIB, Config ROMs, Fonts, Diagnostic Engine Code

[Nyef]

On Wed, 6 Aug 2003, Nyef wrote:

> The two NUPI ROM images are weirder. Each byte of the last 128 is doubled. 
> And this is in both ROMs. I'm thinking that they might be high/low paired 
> 16-bit wide ROMs shared between the NuPI's 68k CPU and the Explorer NuBus 
> requests. Certainly the low 128 bytes of each feels like a 68k interrupt 
> vector table.

Some further research indicates that the NUPI ROMs are the high and low 
parts of 16-bit words. 2238056-5_NUPI has the even addressed bytes, and
2238057-5_NUPI has the odd addressed bytes. An even/odd pairing like this 
is common for 8-bit ROMs used on a 16-bit system such as a 68000. I'm a 
little uneasy about using this mapping for NuBus access, but it looks 
reasonably sane so far for the 68k.

The ROMs are obviously mapped to address 0x000000 on the 68k, and there 
appears to be RAM at 0x180000 for at least 4096 bytes (the initial stack 
pointer in the interrupt vector table points to 0x181000).

Unfortunately, I don't have easy access to a 68k disassembler right now, 
so I don't know too much more.

---------------------------
All programming can be viewed as an exercise.
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Alastair Bridgewater
e-mail: nyef@softhome.net