95 lines
2.7 KiB
Text
95 lines
2.7 KiB
Text
The generic communication protocol for FlightGear provides a powerfull way
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of adding a simple ASCII based or binary protocol, just by defining an
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XML encoded configuration file.
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The definition of the protocol consists of variable separators, line separators,
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and chuncks of text.
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Each chunck defines:
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<name> for ease of use
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<node> the property tree node which provides the data
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<type> the value type (needed for formatting)
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<format> defines the actual piece of text which should be sent.
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it can include formatting options like:
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<type>
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%s string
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%i integer (default)
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%f float
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(not used or needed in binary mode)
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<factor> an optional multiplication factor which can be used for
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unit conversion. (for example, radians to degrees).
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<offset> an optional offset which can be used for unit conversion.
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(for example, degrees Celsius to degrees Fahrenheit).
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The output section also could define the variable separator and line separator.
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The separators can be either a control character such as a tab or newline, or a
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user specified string or other single charachter. The currently supported
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control charachters are:
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<var_separator>:
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<line_separator>:
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Name Charachter
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newline '\n'
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tab '\t'
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formfeed '\f'
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carriagereturn '\r'
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verticaltab '\v'
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any other charachters just need to be added to "Network/generic.cxx"
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The var_separator is placed between each variable, while the line_separator is
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placed at the end of each lot of variables.
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To enable binary mode, simply include a <binary_mode>true</binary_mode> tag in
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your XML file. The format of the binary output is tightly packed, with 1 byte
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for bool, 4 bytes for int, and 8 bytes for double. At this time, strings are not
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supported. A configurable footer at the end of each "line" or packet of binary
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output can be added using the <binary_footer> tag. Options include the length
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of the packet, a magic number to simplify decoding. Examples:
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<binary_footer>magic,0x12345678</binary_footer>
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<binary_footer>length</binary_footer>
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<binary_footer>none</binary_footer> <!-- default -->
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A simple protocol configuration file then could look something like the
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following:
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<?xml version="1.0"?>
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<PropertyList>
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<generic>
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<output>
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<line_separator>newline</line_separator>
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<var_separator>newline</var_separator>
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<binary_mode>false</binary_mode>
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<chunk>
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<name>speed</name>
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<format>V=%d</format>
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<node>/velocities/airspeed-kt</node>
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</chunk>
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<chunk>
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<name>heading</name>
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<format>H=%02d</format>
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<node>/orientation/heading-deg</node>
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<factor>57.29578</factor> <!-- radians to degrees -->
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</chunk>
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<chunk>
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<name>pitch angle</name>
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<format>P=%05.1f</format>
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<type>float</type>
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<node>/orientation/pitch-deg</node>
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</chunk>
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</generic>
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</PropertyList>
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