Overflows in benchmark_rx.py

GNU Radio
1

Hi,

I was running the benchmark scripts with the following set of parametrs

-f 915M -r 5000000 -m psk -8

with 30 dB gain set on both Tx and Rx. I was getting cluttered overflows
and packet received during that time are in error… Like I’m receiving
about a 1000 packet without error and then then system runs into
overflow
and about then quite a large number of packets are received in error.

Output is posted

Demodulator:
bits per symbol: 3
RRC roll-off factor: 0.35
FLL bandwidth: 6.28e-02
Timing bandwidth: 6.28e-02
Phase bandwidth: 6.28e-02
– Opening a USRP2/N-Series device…
– Current recv frame size: 1472 bytes
– Current send frame size: 1472 bytes

UHD Receiver:
UHD Args:
Freq: 915MHz
Gain: 30.000000 dB
Sample Rate: 3.33333Msps
Antenna: None
Spec: None

Demodulator:
bits per symbol: 3
RRC roll-off factor: 0.35
FLL bandwidth: 6.28e-02
Timing bandwidth: 6.28e-02
Phase bandwidth: 6.28e-02

Receive Path:
modulation: psk_demod
bitrate: 5Mb/s
samples/symbol: 2.0000
Differential: True
Using Volk machine: avx_64_mmx
ok = True pktno = 1 n_rcvd = 1 n_right = 1
ok = True pktno = 2 n_rcvd = 2 n_right = 2
ok = True pktno = 3 n_rcvd = 3 n_right = 3
.
.
.
ok = True pktno = 2953 n_rcvd = 2953 n_right = 2953
ok = True pktno = 2954 n_rcvd = 2954 n_right = 2954
ok = True pktno = 2955 n_rcvd = 2955 n_right = 2955
ok = True pktno = 2956 n_rcvd = 2956 n_right = 2956
ok = False pktno = 2957 n_rcvd = 2957 n_right = 2956
ok = False pktno = 2959 n_rcvd = 2958 n_right = 2956
ok = False pktno = 2961 n_rcvd = 2959 n_right = 2956
ok = False pktno = 2963 n_rcvd = 2960 n_right = 2956
ok = False pktno = 2965 n_rcvd = 2961 n_right = 2956
ok = False pktno = 2967 n_rcvd = 2962 n_right = 2956
.
.
.
ok = False pktno = 3838 n_rcvd = 3369 n_right = 2956
ok = False pktno = 3841 n_rcvd = 3370 n_right = 2956
ok = False pktno = 3843 n_rcvd = 3371 n_right = 2956
ok = True pktno = 3845 n_rcvd = 3372 n_right = 2957
ok = True pktno = 3846 n_rcvd = 3373 n_right = 2958
ok = True pktno = 3847 n_rcvd = 3374 n_right = 2959
ok = True pktno = 3848 n_rcvd = 3375 n_right = 2960
.
.
.

Any idea how to avoid these overflows???

2

Hi Tom,

Thanks for the reply… I teed the output at the Rx to a file. It showed
O’s
on my screen, but the file had no O’s. I came to know from a friend of
mine
that the O’s may be going into the stderr and the file had only stdout
output. But the errors you see there were actually preceded by O’s. I
will
run them again after making the changes you suggested.

Thank you

3

On Fri, Feb 15, 2013 at 9:46 PM, Manu T S [email protected] wrote:

– Current send frame size: 1472 bytes
bits per symbol: 3
Using Volk machine: avx_64_mmx
ok = False pktno = 2957 n_rcvd = 2957 n_right = 2956
ok = False pktno = 3843 n_rcvd = 3371 n_right = 2956

Manu T S

This is usually a problem due to the receiver not being able to keep up
with the flow of samples from the UHD device. Try running at a lower
bitrate. If you’re seeing overflows temporarily and then things are
correcting themselves, it looks like you might be right on the edge of
your
system’s capabilities. In this case, it’s like some other process/task
is
taking some time away from your app, causing it to slow down just enough
to
cause problems, but then things look like they come back. You could also
try to run with realtime privileges enabled to make sure your process
gets
priority.

On the other hand, the output you show here doesn’t have any overflow
indication. Are you sure that this is what’s happening? You’re running
at
915 MHz, the center of the 900 MHz ISM band (depending on where you
are).
It’s likely to have other signals in it. Maybe this is just a case of
interference?

Tom