[Coco] Nitros9 L3

[Bill Nobel]

You are right William,   I do have a unreleased version of a early Nitros9 that trapped illegal OP codes, That Curtis and I did, that switched out to system mode when it occurred, never got it to a final release.  I want to see if it is used also in L3

Bill Nobel

> On Nov 3, 2014, at 11:35 AM, William Astle <lost at l-w.ca> wrote:
> 
> 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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>> 
>> 
> 
> 
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