first docu version for raspberry

doc/installation_on_raspberry.md

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+# Installation on Raspberry Pi
+
+To try out, we use an old raspberry pi (first generation).
+
+Install an image on a fresh 16GB SD card, using the Raspberry Pi Imager from https://www.raspberrypi.com/software/.
+Surprise: The imager does not ask for the model of the Raspberry. It just works on the old model. Fine.
+
+In the Imager, we enable the SSH, this makes it possible to work remote on the raspberry.
+
+On PC, we install putty, so that we are able to open an remote shell.
+
+Start putty and connect to the raspberry.
+
+Install samba server on the raspberry, to be able to access the files from remote. https://www.elektronik-kompendium.de/sites/raspberry-pi/2007071.htm
+
+Install wireshark
+sudo apt-get install wireshark
+Choose "yes" for the question whether other users shall be able to trace network traffic.
+
+cd $home
+mkdir myprogs
+cd myprogs
+
+git clone http://github.com/uhi22/pyPlc
+
+git clone http://github.com/uhi22/OpenV2Gx
+cd OpenV2Gx/Release
+make
+
+Test the EXI decoder/encoder
+./OpenV2G DD809a0010d0400000c800410c8000
+./OpenV2G EDa
+
+cd $home/myprogs/pyPlc
+
+Check python version
+python --version
+reports e.g. 3.9.2.
+
+Install the python library for accessing the network interface:
+python -m pip install --upgrade pcap-ct
+also for the superuser (otherwise the import pcap fails)
+sudo python -m pip install --upgrade pcap-ct
+
+Try-out whether the python is able to sniff ethernet packets:
+cd $home/myprogs/pyPlc/tests
+python test_pcap.py
+Result: Fails due to missing permission. This is normal, we need to run with superuser permissions.
+sudo python test_pcap.py
+This should run through loops 0 to 9. If it stucks at Loop 0, the
+patch for non-blocking is missing.
+
+Patch is not needed if we use self.sniffer.dispatch.
+
+Patch the pcap-ct for non-blocking usage:
+Navigate to /usr/local/lib/python3.9/dist-packages/pcap
+cd /usr/local/lib/python3.9/dist-packages/pcap
+Open the file _pcap.py with superuser permissions:
+sudo nano _pcap.py
+Scroll to "def __next__".
+Under the condition "if n == 0: # timeout" replace the line
+continue
+by
+raise StopIteration
+This issue is discussed in https://github.com/karpierz/pcap-ct/issues/9.
+
+Try again
+sudo python test_pcap.py
+This should run through loops 0 to 9.
+
+Problem: Each loop needs around 2 seconds. This is not intended. The 10ms timeout
+seems not to work (timeout_ms=10). On win10, this works perfect.
+On Raspberry, the combination of iterator and non-blocking does not work, see
+https://stackoverflow.com/questions/31305712/how-do-i-make-libpcap-pcap-loop-non-blocking.
+Solution: Change to self.sniffer.dispatch instead of for ts, pkt in self.sniffer.
+
+