[Icc-avr] Doubts using external memory variables

[John Baraclough]

Sorry to be late on this one, but I've been away all day and only 
just switched on my computer.

The original thread can be found here:

  http://dragonsgate.net/pipermail/icc-avr/2007-June/008948.html

There are several things of which you should be aware when using external RAM.

1. The external RAM is much slower than the internal RAM.

2. The compiler will always put the hardware stack in internal RAM 
and then allocate the variables accordingly.

3. The compiler expects the external RAM to be contiguous with the 
internal RAM and the code may not work if there are missing addresses.

Once you understand these three caveats, the best way to proceed is 
to declare that the processor has internal RAM only and manage the 
external RAM yourself using the techniques described in the above 
thread. The appropriate registers will need to be initialised 
correctly as the compiler will not use the startup file   which does 
this for you.

HTH

John 
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