[Coco] DECB -> Pi2/3

[James Ross]

... <snip> ...

> Gene Heskett wrote:
> If its a direct assembly, those limits would still apply I think. 

I understand completely Gene! … It would not / could not, be a line by line translation and it definitely couldn’t be automatic.  However, it could be a structural / functional / block level – translation. It would be a LOT of work for SURE. 

> I would 
> be a bit leery of an assembler that took a 16 bit register and extended 
> it to 32 bits without its calling a sub of some sort to actually check 
> the validity of the added 16 bits.  That would be a bit like a 5 year 
> old poking at a 6 foot Western Diamondback with a 2 foot stick.

> Thats not to say that it can't be done, but it would take some carefull 
> editing of both header files and the assembly code, trying to keep it 
> from becoming one big flat memory mess.  

According the Wiki: "The ARM v7 architecture implements three privilege levels: application, operating system, and hypervisor. Unusually, level 0 (PL0) is the least-privileged level, while level 2 (PL2) is the most-privileged (hypervisor) level.[8]".  Which I believe both the Pi2/3 have v7 or above.  And I am pretty sure they have the ability to shift memory blocks around logically too?  

> That was the root cause of 90% 
> of the crashing the amiga's did back in the day.  Processes scribbling 
> on each others memory and it goes boom.
 
HA! -- good one! 

James