:period vs :sampleRate in Sensor.registerSensorDataListener

flocsy 5 months ago

What is the real meaning of :period and :sampleRate in Sensor.registerSensorDataListener? According to the documentation:

:period - Period of time to request samples in seconds. Maximum is 4 seconds.

:sampleRate - Samples per second to request in Hz.

According to the fr245 simulator I see that :sampleRate sets the rate of my callback function being called. This makes sense.

But what exactly is :period?

Both in case of

:period => 1, :sampleRate => 4

and

:period => 4, :sampleRate => 1

every time my callback is called, each array has size 4. But what are the values? The sentence "Period of time to request samples in seconds." is a bit unclear. My interpretation was that in case of :period: 4, :sampleRate: 1

accel.x[0] would be the x acceleration 0 seconds ago (now),

accel.x[1] would be the x acceleration 1 seconds ago,

accel.x[2] would be the x acceleration 2 seconds ago,

accel.x[3] would be the x acceleration 3 seconds ago,

but looking at the data it seems either I didn't understand it or the fr245 simulator is buggy because if I was right then the data from last second should be similar to the data from this second, except that last second's x[0] should be this second's x[1], etc. But the numbers are completely different.

And why I get arras of size 4 in both cases?

0 Rick 5 months ago

A callback event is triggered once every "period" seconds and that callback data contains period seconds worth of data at the sample rate.

If period = 1 and sampleRate = 25 Hz, then callback is called every second and there are 25 samples in that data

if period = 4 and sampleRate = 25 Hz, the callback occurs each 4 seconds and there are 100 samples in that data.

0 flocsy 5 months ago in reply to Rick

R U guessing? If you read my examples above or better try it for yourself in the simulator then you'll see that what you wrote is not what's happening. At least in the simulator. If that's the way it is supposed to work, then there's a bug in the simulator.

No matter what the period is set to the callback function is being called once a second.

0 Rick 5 months ago in reply to flocsy

I get a Callback every 4 seconds when period is 4, and every 1 second when period is 1.

0 Rick 5 months ago in reply to flocsy

Ok - the above screenshots are from an Epix2 running in the simulator. I just tried on a 245 and you are correct, the event is triggered every 1 seconds even though the period is set to 4 seconds. The other strange thing I'm seeing is that the callback is fired multiple times within the same second.

With period set to 1 second, the callback fires 4 times within the same second

With period set to 2 seconds, the callback fires 2 times within the same second

With period set to 3 seconds, it does this - 1 callback each second for 2 seconds followed by 2 callbacks in 1 second

With period set to 4 seconds,the callback fires each second

Very weird - but everything works in the SIM for me on Epix and Fenix 5,6,7 which is my target audience.

0 flocsy 5 months ago in reply to Rick

OK!!!!! Great! So now it makes sense, and I'll open a bug for the fr245 on the simulator. It's such a shame how much time can be wasted by randomly choosing the wrong device...

forums.garmin.com/.../bug-sensor-registersensordatalistener-doesn-t-correspond-to-the-period-in-the-options-on-fr245-in-the-simulator