FPU FFT nRF52840 Measure elapsed time

[Cecylia]

Hi,

I would like to measure the elapsed time difference between using FPU and not using FPU in my app (nRF52840).  I'm thinking to use the FPU FFT as the base example.  So I enable some sort of timer and measure the ticks elapsed before and after calling fft_process, and then disable the FPU and re-measure.  If this works, then I can use the method to try it on my code.

Questions:
1) Which timer example in SDK 15.3 can be used to measure this?  Better yet, can you upload a modified sample code for nRF52840 DK which would print in the log the elapsed time along with the graph?

2) How do you disable FPU in IAR 7.60.1? Is it to just set the "FPU" option to "None"?

[Jørgen Holmefjord]

Hi,

1. NRF_LOG supports timestamping log messages. If the resolution of this is sufficient for you or not depends on how long the FPU/FFT operations will take. This post shows a possible solution for using RTC. It will probably be much easier to use GPIO toggling and using a logic analyzer to measure the time between the GPIO toggles. This is what we typically use for time-measurements.

2. I believe this should be sufficient, yes.

Best regards,
Jørgen