[CST-2] Comp. Arch 1998.7.3 - backwards compatibility problems

[Jonny Graham]

> Does anyone have any further points to add, criticism/corrections to make,
> or answers to my questions?

The ARM exposes the pc, such that it always points 3 (or is it 4, I 
don't remember...) instructions ahead of the one currently being 
executed. Extending the pipeline to improve performance means that the 
pc would naturally point even further ahead which would break existing 
code. The solution is to hide the real pc and expose a 'psuedo-pc', 
pointing the expected distance ahead of the currently executing instruction.

Jonny

> 
> Cheers,
> George
> 
> Soon to be gbmvdd@cantab.net
> 
> 
> 
> 
> _______________________________________________
> CST-2 mailing list
> CST-2@srcf.ucam.org
> http://www.srcf.ucam.org/mailman/listinfo/cst-2