Problem with USRP2 continuous transmission at >10MHz

GNU Radio
1

Hi,

We use tx_samples.cc to transmit a file with 16bit-short complex samples
at
10MHz and 20MHz. We use another USRP2 to receive the signal and store on
disk. We observed there are some unexpected gaps in the received
samples.
Using usrp2_fft.py with the osiliscope view, we also observed such kind
of
gaps.
We guess this might be caused by underrun at the transmitter side. We
use
the delievered ethernet cable, so this shouldn’t be the problem of bad
cable.
Anyway, how can we transmit samples contineously and stably without
underrun
at 20MSamples/s??

Thanks in advnced.

Bests,
Hanwen & Christoph

2

hanwen wrote:

Anyway, how can we transmit samples contineously and stably without
underrun at 20MSamples/s??

1 – Make sure you have realtime scheduling enabled
2 – Use a very fast computer

are you sure you are seeing underruns? Have you connected to the debug
serial port on the USRP2 and seen it send “U”?

Matt

3

Hi,

From: Matt E. [email protected]

are you sure you are seeing underruns? Have you connected to the debug serial
port on the USRP2 and seen it send “U”?

Matt

USRP2 has 6 leds. Two of them are ON when every thing is OK. Can you use
one/two of others to indicate over/under run?

Best Regards,

Firas

4

Hi Matt,

thanks for the advice. We connected the serial port and couldn’t observe
the
underrun message and we enabled the realtime scheduling but there was no
improvement. Strangely enough after that the program only works without
interrupts if it is started as su in a shell and if this shell window
is put
in the background of the desktop (meaning that another window is the one
we
are working in right at that moment).

We are using Ubuntu 9.04 with the latest trunk version of gnuradio but
don’t
know enough about the OS realtime scheduling issue to explain it. Does
anybody
have more knowledge about ubuntu and realtime to explain this
behaviour?

Regards,

Hanwen and Christoph

5

Hi,

From: Christoph T. [email protected]

We are using Ubuntu 9.04 with the latest trunk version of gnuradio but don’t
know enough about the OS realtime scheduling issue to explain it. Does anybody
have more knowledge about ubuntu and realtime to explain this behaviour?

Regards,

Hanwen and Christoph

The realtime scheduling can be only used/enabled by administrator (using
sudo).

Best Reagrds,

Firas