[Discuss-gnuradio] gnuradio transmission delay

[Phelps Williams]

I have a simple bpsk transmitter setup with a custom udp source block
which outputs a fixed pattern if no data is available from the socket.
 I have instrumented the block to indicate when data is read from the
socket inside of work().

My radio looks like this:
Custom UDP Source -> DPSK Mod (DBPSK, 10 samp/sym) -> Multiply Const
(0.3) -> UHD: USRP Sink

My sample rate is 1e6.

I can tell from my instrumented UDP Source that udp traffic is handled
by work and passed on almost immediately.  However I can tell from
both monitoring the spectrum and the receiver output on the other side
that the data takes between 7 and 10 seconds before I see the expected
output from the N200.  I thought this could be improved by reducing
the maximum socket buffer size (sudo sysctl -w
net.core.wmem_max=5000000) but that didn't seem to make a difference.
I went as low as wmem_max=10000 with no difference in delay.  My goal
is to get the total delay to < 1sec.

What else could be adding delay to my transmission path?  Are there
other buffers I can tweak?  Where else should I be looking?

-Phelps