[Hackrf-dev] communication problem HACK RF - LINUX

[Simone Ciccia S210664]

Goodmorning,

I'm experiencing issues with my HACK RF just feeding samples in a
simple gnuradio flowgraph, HACK-RF SOURCE -> NULL SINK, in Linux 
12.04LTS

For sample rate above 10MHz I get continuous Overrun ("O").

Hack RF is interfaced with the PC through the USB 3.0 port, and the 
tests on it (i.e. with hackrf_transfer) indicates that works correctly 
at 20MHz.

==============================================================
hackrf_transfer -r /dev/null -s 20000000
call hackrf_sample_rate_set(20000000 Hz/20.000 MHz)
call hackrf_baseband_filter_bandwidth_set(15000000 Hz/15.000 MHz)
call hackrf_set_freq(900000000 Hz/900.000 MHz)
Stop with Ctrl-C
40.1 MiB / 1.000 sec = 40.1 MiB/second
39.8 MiB / 1.000 sec = 39.8 MiB/second
40.1 MiB / 1.000 sec = 40.1 MiB/second
36.7 MiB / 0.916 sec = 40.1 MiB/second

User cancel, exiting...
Total time: 3.91699 s
hackrf_stop_rx() done
hackrf_close() done
hackrf_exit() done
fclose(fd) done
exit
=====================================

Searching for the problem I found it could be the Linux buffer size,
thus I set the file sysctl.conf as follows,

# Updates for Gnu Radio
net.core.rmem_max = 50000000
net.core.wmem_max = 1048576
kernel.shmmax = 2147483648
net.ipv4.tcp_rmem= 10240 87380 12582912
net.ipv4.tcp_wmem= 10240 87380 12582912
net.core.netdev_max_backlog = 10000
net.ipv4.route.flush=1
net.ipv4.tcp_sack=0

but it does not solve!

Anyone have already encountered/solved such issue?

I appreciate any help/idea,
best regards
simone