rtl_test -p x establishing freq correction

[Ben Hiett]

does anyone know how rtl_test -p works (or am i going to have to read the
src code ;-)

I ran it for 60s as follows:

***@esroe-5:~/rtl-sdr$ rtl_test -p 60
Found 1 device(s):
0: Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6
19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9
44.5 48.0 49.6
Sampling at 2048000 S/s.
Reporting PPM error measurement every 10 seconds...
Press ^C after a few minutes.
Reading samples in async mode...
real sample rate: 2048274 current PPM: 134 cumulative PPM: 134
real sample rate: 2048194 current PPM: 95 cumulative PPM: 114
real sample rate: 2048271 current PPM: 133 cumulative PPM: 120

I assume the current is the value computed from the last 10s and the
cumulative is a 'running' mean.

I guess the idea is that you use the cumulative ppm as an arg when running
rtl_fm, rtl_power or whatever other app you are using (if it has the
ability to apply a correction to the tuner)?

I think it may have crashed as it only reported 3 readings, I have noticed
that my dongle seems a bit temperamental, I often get errors like this:

Using device 0: Generic RTL2832U OEM
rtlsdr_write_reg failed with -1
Resetting device...
rtlsdr_write_reg failed with -4
rtlsdr_write_reg failed with -4
rtlsdr_write_reg failed with -4
rtlsdr_write_reg failed with -4
rtlsdr_write_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4