Coldfire AGAIN

[Fats]

biggun wrote:

Question was: Can trashing Chipmem trash the system


Answer: Yes.
There is more than pictures in chipmem.
For example, there are Copperlist in chipmem.
If you thrash the copper list then the copper couldeven  *fuck* up the Disk DMA.
In Chipmem could be IO buffers where disk-IO read/writes too.
 
...

The orignal AMIGA allowed usage of DMA and Blitter to accelerate the system.
If you need to check ranges for each blitter call the overhead will be HUUGEE!

You could do the same trick in the copperlist, DMA and blitter as was done by the MMU. You could design the SuperAGA chipset in such a way that the OS can say to the chipset what actions are allowed by certain tasks like the MMU allows to limit access to certain memory areas. This would normally not impact speed as it is done in parallel. Only when some non-allowed action is asked an exception is raised, just like an exception is raised by the MMU when a wrong memory address is accessed.
This would work best when the SuperAGA and CPU are integrated in one chip.

greets,
Staf.

[Fats]

biggun wrote:

A Blitter that has a MMU will be extremly expensive to build and its performance will be dissapointing.
Using the Blitter will have a huge overhead as your MMU Blitter table will need to be replaced when switching tasks.

Please get a clue about the HW costs of implementing an MMU  and the overhead of maintaining the MMU tables by the OS.

I don't think you need a full blown MMU. I think one or a few mask registers can do the trick. Page paged tables are needed when implementing virtual memory and page swapping which is not needed in this case.

greets,
Staf.