add Readme

README.txt

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-hi
+Hi!
+
+This is a collection of custom blocks that are not directly associated with a
+special project. For sample applications see:
+
+https://github.com/bastibl/gr-ieee802-11
+https://github.com/bastibl/gr-ieee802-15-4
+
+
+
+### Wireshark Connector
+
+This blocks outputs PDUs in the PCAP format. The resulting file can be opened in
+nearly all network monitoring applications. Some examples are Wireshark, Tshark,
+and tcpdump. Currently, it support WiFi packets with radiotap header and ZigBee.
+
+Since GNU Radio does not support File Sinks that append to a file, one can not
+open Linux pipes / fifos. For that reason, it is not easily possible to monitor
+traffic live. However, loading the file in Wireshark works.
+
+I made a patch that adds an append option to the File Sink. If you are
+interested see:
+https://github.com/bastibl/gnuradio/commit/befa5bd94b59a56e13d7ec4fe0da86637fe624d9
+
+For further information about radiotap, pcap, and Wireshark see:
+http://www.radiotap.org/
+http://www.wireshark.org/
+
+
+
+### Burst Tagger
+
+Tags a burst / packet with tx_sob und tx_eob tags. This is useful if the SDR is
+operating in half duplex mode. With adding a tx_eob the USRP switches back to
+receive mode immediately. That way, direct responses like ACKs are not missed.
+
+The block searches for a special tag that indicates the start of a burst. The
+name of this tag is configurable. The tag should indicate the length of the
+packet in samples. Also a multiplier can be specified, which multiples the
+length given in the tag.
+
+
+
+### Packet Dropper
+
+Drops a configurable percentage of messages. I used it to test protocol logic
+like ACKs, retransmission and stuff.
+
+
+
+### Packet Pad
+
+Adds a configurable number of zeros before and after a burst. The burst has to
+be started with an tx_sob, and ended with a tx_eob tag.
+From time to time I had issues when I did not pad the sample stream. This block
+helps to investigate that.
+Also it is handy for loopback testing when there is no continues sample stream.
+
+
+
+### Periodic Msg Source
+
+This block sends messages at regular intervals  much like the message strobe block in
+mainline GNU Radio. With this block you can in addition configure the number of
+packets that are sent. When all normal messages are sent, the blocks sends a final
+PMT_EOF message to indicate that it is done.
+
+I used this block for performance tests with no-GUI flow graphs. This way it is
+possible to shout down no-GUI flow graphs with message blocks. As far as I know,
+this is not possible with mainline GNU Radio. For that reason, I created a patch
+that checks if the block is done after a message was handled. See
+
+https://github.com/bastibl/gnuradio/commit/75a22cb8c10d867a68c8849bf56a0aa3906df266
+
+
+
+### Dependencies
+
+GNU Radio v3.7
+
+
+### Installation
+
+git clone https://github.com/bastibl/gr-foo.git
+cd gr-foo
+mkdir build
+cd build
+cmake ..
+make
+sudo make install
+sudo ldconfig
+