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How to determine pipeline refill cycles

Question asked by Mike Simmonds on Oct 25, 2016
Latest reply on Nov 4, 2016 by Mike Simmonds

The ARM Cortex M3 Technical Reference Manual R2P1 states ...

P  The number of cycles required for a pipeline refill. This ranges from 1 to 3
depending on the alignment and width of the target instruction, and whether the
processor manages to speculate the address early.

So firstly what CPU revision is used in the LPC1313? In case it matters.

 

But, more importantly, how can we know if the processor speculates the address

early or not and how, numerically, does this effect the pipeline refill.

 

We know that the Cortex-M3 prefetches 32-bit aligned 32-bit words and we can

lookup the width of the target instruction; but some clarification about cycle counts

(with examples) would be appreciated. [Presumably, we could use the cycle count

display in the debugger to evaluate the alignment and width factors, but the 'speculation'

component need -- detailed -- explanation.]

 

Background: I want to construct a precisely timed busy loop (in assembler naturally).

Of the order of 2 micro-seconds.

 

Regards, Mike.

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