I just solved this problem!
The reason is that in gnuradio-examples, UDP default payload size is set to
1471. In gr_udp_source.cc, all received data will be round down to a
multiple of d_itemsize. Since sizeof_gr_complex is 8, so only 1464 Bytes are
received correctly, while the left 7 byte are abandoned. This will
in turn disturb the position of the following data stream, and also
affect the mmse_fir_interpolator and make imu negative.
Actually, the default UDP payload size in gr_udp_source.h is set to 1472, but
in
examples, it is set to 1471. I am not sure if this is a bug. A simple way to
bypass this problem is to set MTU
size as a multiple of itemsize, such as 1464 or 1472, then everything
works as expected.
________________________________
发件人： Zhen <zkon...@yahoo.com.cn>
收件人： "discuss-gnuradio@gnu.org" <discuss-gnuradio@gnu.org>
发送日期： 2011年6月28日, 星期二, 上午 2:34
主题: [Discuss-gnuradio] Error on "Assertion `imu >= 0' failed" when using
gr.udp_source/sink
Hello,
I modified "benchmark_tx.py and benchmark_rx.py" by replacing the
usrp_source/sink with gr.udp_source/sink and gr.file_source/sink, to see if the
generated IQ data from tx side can be correctly captured and processed at rx
side via UDP socket or trace file instead of USRP. If it does, then I can
analyze the signal off-line or transmit the captured data to others via socket.
The modified program with gr.file_source/sink works correctly and the results
are exactly the same when using usrp_source/sink.
But when using
udp_source/sink, the tx side can send packets to udp_sink well, but the rx
side program is aborted with error
"python: gri_mmse_fir_interpolator.cc:71: float
gri_mmse_fir_interpolator::interpolate(const float*, float) const:
Assertion `imu >= 0' failed."
My python codes are configured like the following:
rx side:
----------------------------------------------------------------------
self.u = gr.udp_source(gr.sizeof_gr_complex, options.host, options.port,
options.packet_size, not options.no_eof, not options.no_wait)
rx_path = receive_path.receive_path(demod_class, rx_callback, options)
self.connect(self.u, rx_path)
---------------------------------------------------------------------
tx side:
------------------------------------------------------------------
self.u = gr.udp_sink(gr.sizeof_gr_complex, options.host, options.port,
options.packet_size,
options.no_eof);
tx_path = transmit_path.transmit_path(modulator_class, options)
self.connect(tx_path, self.u)
------------------------------------------------------------------
Then I added a printf in "gri_mmse_fir_interpolator.cc", and found imu is
−2147483648, .i.e, -0x80000000;
But in normal situation when using usrp_source/sink or file_source/sink, it is
between 63--67.
I searched the mailing list and knew that the imu value is used to tell the
interpolating filter where in the filter to takethe output from, but got few
clues to solve this problem.
I wonder if udp_source/sink modifies the complex data stream it transmits then
the gnuradio can't process it correctly?
Or is there any suggestion to solve it?
Thanks in advance!
Zhen
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