just a quick question, have you coded the loop in machine code or C. If in C have you checked the machine code it produced. Non optimized code in GCC for instance can easily make a simple loop toggling an led into ten cycles of machine code. I'm assuming no optimizing is going on as a for loop that does nothing would probably be optimized out unless you put a "nop" instuction in it. Either look at the machine code or add an increasing number of nops into the loop to see what each one adds to the time. It may not be as linear as expected due to pipe lining and instruction aligning. Paul.
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