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[Discuss-gnuradio] Piping to the USRP - mkfifo issue

From: Tom Hendrick
Subject: [Discuss-gnuradio] Piping to the USRP - mkfifo issue
Date: Sun, 6 Mar 2011 15:59:58 -0800 (PST)


  I am using a web camera to get an MPEG-4 rtsp stream that is set to a constant bitrate.  I have a script which pipes the rtsp stream to a code in C++.  The C++ code modulates the signal and writes  a .WAV file to the hard disk.

I have a python script which interfaces with GNURadio/USRP which I created using GRC.  This takes a file stored on the hard disk and outputs the analog waveform on the output of the USRP and I run this in a second terminal window.

Everything works on the transmitter side, except that I have a file that is constantly increasing in size, and the USRP script starts from the beginning of the file and plays for a certain time before stopping.  If I restart, it does it longer and longer each time as expected since the file is increasing in size.  I verified I have gotten an output on the USRP using an oscilloscope and it looked fine.

I wanted to try and use piping with mkfifo.

When I erase the file that is written/read from with the couple of scripts I have, I then use mkfifo temp.wav (where temp.wav is my .wav file). 

Then I start my scripts that pipe the camera output to the temp.wav file.  In a second terminal window I then run my USRP script and it seems to open the file but I don't get any output on the USRP.

Has anyone encountered this problem?  I'm not sure what could be wrong, but it works with a normal file as I described above. Any suggestions?

Thanks for your help!

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