RT Timed Loop accelerated thanks to RT Trace Tool. Why?

[mateusz_owczarek]

Dear All,

I'm using Real-Time Trace Viewer VIs to trace the execution of my program.

I noticed very very curious thing that surprised me a lot and I can not explain why it works like that.

I got a VI that reads acceleration values from accelerometer connected to myRIO via I2C.

The acquisition task is placed inside RT Timed Loop with default parameters. 

I noticed that when I run my VI without RT tracing, the iteration duration of the loop is ~30ms.

However, when I enable tracing (put Start Trace before the loop and Stop Trace and Save after), the times are even 10x faster! The same loop has duration ~3ms! 

I believe that this phenomenon has an easy and silly explanation, but I haven't found it so far 🙂

I hope you can help me! Thanks in advance!

I attached the VI. 

Here you can find a screenshot ('false' cases are empty, just have error wire)

Software:

LabVIEW 2014

LabVIEW RT 2014

LabVIEW FPGA 2014

I2C&SPI API v3.0.0.22 by National Instruments from VIPM

Hardware:

myRIO

Best Regards,

Mateusz

[PiDi]

Check if there is no error on the wire when you're inside timed loop after enabling trace.

[mateusz_owczarek]

Thanks, but there is no error. Furthermore, I can see on charts that incoming data are correct and are coming much faster when tracing is enabled.

I'm attaching demonstration video to make it clearer. 

https://www.youtube.com/watch?v=2XcBAP5vI_4&feature=youtu.be

[PiDi]

Ok, this is strange. I have no idea what's going on there :?