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Generic protocol: Difference between revisions
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FlightGear has an inbuilt "generic" protocol to push and pull data. (todo) | FlightGear has an inbuilt "generic" protocol to push and pull data. (todo) | ||
To interface with FlightGear on a socket for example, the following steps need to be taken | To interface with FlightGear on a socket for example, the following steps need to be taken: | ||
# Establish which "properties" you want to appear "on the wire" | # Establish which "properties" you want to appear "on the wire". | ||
# Create a my_protocol.xml file containing those properties | # Create a <code>my_protocol.xml</code> file containing those properties. | ||
# Start | # Start FlightGear with the generic protocol option using <code>my_protocol</code> sent through the network socket. | ||
For this simple example say were interested in heading and altitude, and we want to "listen" ie output to a socket at port 6789, | For this simple example say were interested in heading and altitude, and we want to "listen" ie output to a socket at port 6789, UDP and receiving 10 times a second in the format: | ||
alt\thead\n | alt\thead\n | ||
// ie altitude - tab - heading - newline | // ie altitude - tab - heading - newline | ||
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[[$FG_ROOT]]/Protocol/my_protocol.xml | [[$FG_ROOT]]/Protocol/my_protocol.xml | ||
Edit the <code>my_protocol.xml</code> file and write in it: | |||
<syntaxhighlight lang="xml"> | <syntaxhighlight lang="xml"> | ||
<?xml version="1.0"?> | <?xml version="1.0"?> | ||
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* The '''output''' tag indicates the protocol for output. The same "protocol" file can contain an "input" section, absent in this example (more later). | * The '''output''' tag indicates the protocol for output. The same "protocol" file can contain an "input" section, absent in this example (more later). | ||
* '''line_seperator''' - the end of line (todo | * '''line_seperator''' - the end of line (todo - is this <code>\r\n</code>?) | ||
* '''var_seperator''' - the delimiter for the properties, this could be "|", "###", any string. | * '''var_seperator''' - the delimiter for the properties, this could be "|", "###", any string. | ||
* The two '''chunk''' blocks contain our data. Note that these appear in the order presented within the | * The two '''chunk''' blocks contain our data. Note that these appear in the order presented within the XML file. | ||
** '''node''' - the node of data we want | ** '''node''' - the node of data we want | ||
** '''name''' - it there for a reference, its not transmitted and note necessary (like a note) | ** '''name''' - it there for a reference, its not transmitted and note necessary (like a note) | ||
** '''type''' - the way this xml is to interpret the value. This is quite important tag. For example if its not there or a string, then "floats" go wild and end up being a string of 32 characters with two decimal places! | ** '''type''' - the way this xml is to interpret the value. This is quite important tag. For example if its not there or a string, then "floats" go wild and end up being a string of 32 characters with two decimal places! | ||
** '''format''' - same syntax as printf | ** '''format''' - same syntax as <code>printf</code> function in C/C++ | ||
** There's more that can be done {todo - link to a full blown example/reference} | ** There's more that can be done {todo - link to a full blown example/reference} | ||