measure time using FTM input capture

rodolfocazares — Wed, 13 Sep 2017 16:53:20 GMT

I am using micro kinetis MKE02Z64VLC4 to measure time trougth FTM input capture. Project was initied on process expert.

I need to reset counter in each event and I call

** ===================================================================
** Method : EncoderA_Reset (component Capture)
** Description :
** This method resets the counter register (see implementation
** note in <General Info>).

But counter is not reset.

Where I can see how I need implement it ??

Re: measure time using FTM input capture

egoodii — Wed, 13 Sep 2017 21:32:20 GMT

You don't describe exactly what *kind* of time you are measuring, but in any case it is FAR better NOT to reset the counter during operation, as you will most likely run into race conditions and/or inconsistent measurements. Let the counter free-run (modulo 65536) and simply use unsigned 16-bit math to calculate elapsed time. I measure time between sequences of rising edges, and each period is simply:

elapased_u16t = new_timestamp_u16t - old_timestamp_u16t; //timestamps pulled from capture register

The unsigned math will always give the proper difference, even including one rollover. It gets 'messier' if your time period math has to include a timeframe longer than one FTM rollover, as you have to start keeping track of overflow interrupts and THOSE race conditions will give you some headaches...

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measure time using FTM input capture

Re: measure time using FTM input capture