Reducing the latency in tunnel.py

Hi all,

I would like to send a MAC layer control packet every 4 ms from computer
A
to computer B to tell B when to send data using USRP and GNU Radio. It
is
like TDMA and a frame is 4 ms. I am trying to do this work by modifying
tunnel.py in the gnuradio-example folder. I removed the carry sensing
part
and added the control packet in the tunnel.py.

I enabled the real-time scheduling. I set nice= -18, fusb_block_size =
512,
fusb_nblocks = 2, modulation=gmsk, and bitrate =1Mb/sec.

OS: 2.6.29.6-217.2.7.fc11.i586
CPU: 2.8 GHz
Gnuradio: (latest development code 3.2.X)

I used two computers and ran the modified tunnel.py on each computer.
For
the test, in the main_loop (main loop for MAC) of tunnel.py I generated
one
byte payload ( I sent the one byte payload chr(0x00) for 10 times) to
print
the tx time on one computer and rx time on anther computer. I used
software
to make two computers have the same system time. The tx time (at
computer A)
– rx time (at computer B) of the payload is about 5ms. I am wondering
why it
takes so long to send one byte payload and to decode the one byte
payload.
Through the test, I think I cannot implement a TDMA that a frame is 4
ms. I
have tried what I can do to reduce the (tx time – rx time) value.
However,
no luck. Could anyone please give me some hints? Should I just give up
this
way and try to use the in-band singalling? Any suggestions will be
greatly
appreciated!!

Best.
Jane

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