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Controlling/Changing the endianess

Especially in parts of the PROFINET protocol, the endianess needs to change througout the protocol stack. So our current approach with one fixed endianess doesn't work well in this case. I've tried using manual fields, but the result was everything but ideal. 

In general I've encountered multiple situations:

• One layer of the protocol stack is fixed to a given endianess (UDP is Big Endian, for example, PROFINET IO CM Blocks are Big Endian too)
• Endianess of fields are dependent on some parsed values (In DCE/RPC there is a 4 bit field, that controlls if the following fields are BigEndian or LittleEndian)
• Endianess of all fields of a complex type are dependent on the endianess of the parten (In case of PROFINET IO CM the ProfinetIO CM packet has the same endianess of the DCE/RPC packet that contains it)