[Coco] Nitros9 L3

[William Astle]

I should point out that the trap won't help if it fires in user space 
since the kernel won't be mapped at the time it occurs.

An argument can be made that if the trap fires in kernel code, there's a 
bug in the kernel anyway and it's going to be crashing regardless.


On 14-11-03 10:30 AM, Bill Nobel wrote:
> Oh, your right….  I forgot about the 6309 trap vectors.  But I see that in Nitros9 module 3 values are stored.  $10ff @ $0000, $0008 @ $0002 & $20fe @ $0004 not sure as to the reason yet.
>
> Bill Nobel
>
>> On Nov 3, 2014, at 9:24 AM, Robert Gault <robert.gault at att.net> wrote:
>>
>> Bill Nobel wrote:
>>> Yes, I saw those defs, but I notice in my disarm of Nitros9 module that it
>>> uses System DP starting at $0000 which was def’d in level 2 as FHL/Isted
>>> WD1002-05 base address.  It is used now as pointers to I'm assuming
>>> SCF/RBF base addresses.
>>>
>>> <snip>
>>> Bill Nobel
>>>
>>
>> Bill,
>>
>> All the source code I've seen for Level3 assumes a 6309. The 6309 requires a trap for illegal coding and uses the address at $FFF0 to jump to the code. Tandy never used that (6809 only) so the ROM at $FFF0 reads $0000.
>> Given the above, a 6309 requires some code at $0000 to at least jump to the actual trap routine.
>>
>> You could try leaving out any trap code but that would be risky. Sooner or later something will go wrong and vector to $0000 assuming there is valid code at that location.
>>
>> Robert
>>
>>
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>
>