David Laight wrote:

> Woudn't it be better to dereference a pointer to a volatile memory location
> inside the loop - that way the compiler isn't allowed to optimise the
> loop away.
> 
The volatile variables seem to be enough for now. Although I can see a 
cleverer optimiser requiring the fix you propose.

A better fix would be to actually use a hardware timer. If I can figure 
out a way of doing that on acorn32 I'll see if I can fix the routine so 
that it no longer depends on the delay loop at all.

Mike