[Gllug] Beagle Board

[Peter Corlett]

On 12 Jan 2009, at 18:41, Andrew Farnsworth wrote:

> Ok, so I over simplified a bit.  Yes, you can do it on the older  
> hardware but it was not directly supported by the CPU, unlike  
> today's CPUs or even those from the 68030 (68020 even maybe, but it  
> didn't have a separate mmu which the 030 did) did.

You could add the 68851 external MMU to the 68010 and 68020. However,  
you don't require a MMU to do pre-emptive multitasking. You need it  
for virtual memory and memory protection.

> These CPUs had a hardware interrupt that regularly tripped and was  
> easily used for preemptive multitasking.  It is/was possible to do  
> on older hardware, but it was not standard across the board by any  
> stretch of the imagination.

No. The 680x0 CPUs do not generate their own timer interrupt. The  
interrupt normally comes from a dedicated timing chip such as a VIA.  
The 6522 was one such chip, appearing in such diverse systems as the  
BBC B and the Amiga.


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