[Discuss-gnuradio] Choppy Audio from uhd_rx_nogui on a VM

[Shepard Siegel]

This is a simple question with a long prelude.

We have a handful of N210/WBX that work great with UHD with which we
are familiar. Until last night, I had not spent more than ten minutes
with GNU Radio. This morning I installed a fresh Fedora-16 guest VM
running on VMware Workstation on a strong Win7-64b host. I used
build-gnuradio to install GNU Radio 3.6.0 . And in twenty minutes with
no issues whatsoever, I’m feeding our RF signal generator into a USRP2
and making sane GUI comparisons to our spectrum analyzer. Brilliant!

address@hidden ~]$ uhd_fft -a addr=10.0.209.194  -f 935M -s 2M
linux; GNU C++ version 4.6.3 20120306 (Red Hat 4.6.3-2); Boost_104700;
UHD_003.004.002-133-gb61a1103
-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
Using Volk machine: avx_64

I then experimented with the uhd_rx_nogui program and found that the
audio is discontinuous (though almost intelligible), as is shown by
the stream of audio underflow indications that feed to stdout:

address@hidden ~]$ uhd_rx_nogui -a addr=10.0.209.194 -f 99.5M -m FM
linux; GNU C++ version 4.6.3 20120306 (Red Hat 4.6.3-2); Boost_104700;
UHD_003.004.002-133-gb61a1103
-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
UHD Warning:
    The hardware does not support the requested RX sample rate:
    Target sample rate: 0.256000 MSps
    Actual sample rate: 0.255102 MSps
>>> gr_fir_ccf: using SSE
Using gain:  19.0
>>> gr_fir_ccc: using SSE
>>> gr_fir_fff: using SSE
aUaUaUaUaUaUaUaUaU … aUaUaUaUaUOaU

I’m uncertain if this is my clueless-ness of audio with the Fedora VM
under VMWare; or something more GNU Radio related. Audio seems work
fine in the VM. And GNU Radio seems to work fine (no errors, good
data) writing files with uhd_rx_cfile. Is this issue likely a VM audio
device issue? Am I “off in the weeds” running GNU Radio audio on a VM?
This isn’t my day job; but any guidance on bisecting this issue is
appreciated.

-Shep