Cortex-R4 PMU CP15 cycle counter value : runto readout vs step by step to readout..

Looking at this cycle counter value, and  as they say starring at it with blank mind .. not understanding it. 

Very seems trivial setup: I just enable it early at startup,  just after my PLL's all set and locked, and CPU clock is set to final speec & runs Ok..
I init, reset , & start the cycle counter, it runs .

Then in main(), I set break point & read it out.  Ok, it ticked many times,  Too many for my liking.. Looks abnormally high.  So I decide to reset, and go step my step (C statements .. or asm, wont' matter..), hoping I will see where it takes most cycles, thinking RAM init, or C runtime copying.

..And i get to same break point in main, and it's different, Massively different to if I just let it run.   (Repeated the process just incase).

E.g. if I just let it run,  cycles = 1,656,559;    If I step-by-step from cp15/cycle counter init to the main brkpt,  cycles = 106729,  or like 15 times less..

What Am I seeing /not ..?  What black magic happens while I step , I cannot rationalize.  

The bigger figure is /cannot be correct (if it is, its a horrible hal & c init runtime load times; and I will throw it the f away, I cannot have this long boot).  The smaller figure from step-by-step is what I intuitively expect ( or want.)

Now I'm left with good-old toggle gpio & scope it ,  from as early as possible.

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  • Next hint: How about running chunks of your code instead single stepping each instruction.

  • Phew,  thanks for hints.  This made my morning.  ( I think it's really bad looking at code past 10 pm ..)

    So what I was blind to see, is when I step / step over some self tests, when it breaks say as something like, while (self test not done..),  when I step next that peripheral /module sure will finish next I resume execution.

    E.g. it starts memory self-test controller diagnostic then busy waits in while(), then  checks PBIST ROM, and waits for that test complete, and few others.. Overall lots of busy waiting, but they do need to be done.

    So now I need to think about how I'm gonna boot under 10 ms...

    Thank you for help.

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  • Phew,  thanks for hints.  This made my morning.  ( I think it's really bad looking at code past 10 pm ..)

    So what I was blind to see, is when I step / step over some self tests, when it breaks say as something like, while (self test not done..),  when I step next that peripheral /module sure will finish next I resume execution.

    E.g. it starts memory self-test controller diagnostic then busy waits in while(), then  checks PBIST ROM, and waits for that test complete, and few others.. Overall lots of busy waiting, but they do need to be done.

    So now I need to think about how I'm gonna boot under 10 ms...

    Thank you for help.

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