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How to get the actual value from MPC574xG STM counter ?

Question asked by Martin Schultheiss on Jan 29, 2018

Dear NXP Support,

 

we're using the STM module of the MPC574xG as the driver for an high resolution counter. The resolution of this counter should be one timer tick. Therefore we need to get the hardware counter value as accurate as possible.

In MPC5748G Reference Manual, Rev. 5, 12/2016 you describe the following:

 

NOTE
Due to two clock sources and different clock domains, Values
in this field can lag behind the internal counter value for up to
six system plus eight counter clock cycles. Therefore, the value
read from this field immediately after may be lower than the
actual value of the internal counter.

 

For us it is not quite clear what this means and how we can get the actual HW counter value.

E.g. is there a worst case scenario (e.g. add eight ticks to the read value...)?

The solution has to be independent from frequency configuration, because our customer can configure the core and peripherals according to his needs.

 

Thanks in advance and best regards

Martin Schultheiß

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