WIP: add dropout check to fft plotter

[kd0aij]

we're regularly dropping every 10th accel sample. Need to check whether this is happening at the sensor, or just in the log:

sample range:  4382 38370
N samples:  33988
ndeltas:  33987
duration: 37.785 seconds
average sample rate: 899 Hz
mean sample interval:  1.11 msec
std:  342 usec

[kd0aij]

resampling using numpy.interp, appears to have added harmonic distortion. This is likely due to using the SampleUS values as timestamps. Will have to preprocess them to remove the jitter before resampling.

[kd0aij]

this version assumes the SampleUS fields in ACCn and GYRn log records are sequential sample counters representing the total number of samples received from the sensor in fast_sampling mode since the last fifo error or reset. It also computes the sample rate by comparing SampleUS to the timestamps (TimeUS)

[kd0aij]

the hardwired sample rates don't look right for fmu-v4