Hi,
I encountered this strange behavior when running fl2k_test on Windows 7: basically after a while the sample rate drifts and speeds up considerably. Sometimes it even starts up directly like that.

In the command prompt I get:
C:\Users\Francesco Gugliuzza\Downloads\Sviluppo\FL2000fl2k_win_2018-08-09>fl2k_test.exe -s 138e6
Reporting PPM error measurement every 10 seconds...
Press ^C after a few minutes.
real sample rate: 146656386 current PPM: 62727 cumulative PPM: 62727
real sample rate: 150803676 current PPM: 92780 cumulative PPM: 77858
real sample rate: 149716182 current PPM: 84900 cumulative PPM: 80218
real sample rate: 150107883 current PPM: 87738 cumulative PPM: 82104
real sample rate: 150526750 current PPM: 90774 cumulative PPM: 83843

The same thing happens if I compile the latest osmo-fl2k myself using Cygwin.
I'm running everything on a laptop with an i7 4710HQ CPU and 8 GB of ram, and I'm using a RayCue HDMI+VGA box.

Do you have an idea why the real sample rate drifts so much?

Thanks!

--
Francesco Gugliuzza