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OPUS Projektor Manual
Variables
4
Variables
The main approach followed in the program is to create pages and the navigation between
them which is a more static definition.
The dynamics come in with variables changing their values. Other tools use the term "signal"
instead of "variable" to describe the same thing. A CANopen "object" also describes what we
call a "variable" here. The same is true for J1939 "Suspect Parameter Numbers (SPNs)".
This page provides an overview of the general concept behind the variables.
There are follow-up pages explaining the menus and dialogs to create and manage variables
owners and variables .
Owner Concept
Every variable in the GUI designer has to have an owner assigned. The owner is the only
one controlling the value of the variable.
If somebody else tries to write the value of the variable this is considered a write request
which is forwarded to the owner of the variable.
Only if the owner confirms the new value by providing an update of the variable it is
considered changed.
If the variable is expected to be frequently updated by the owner e.g. via CAN bus
message then they can also be considered invalid if the update does not arrive in time.
Types of Owners
Generally there are two different types of owners:
·
Remote ECUs connected via CAN bus
·
Other programs/processes running on the display.
Examples of the second type are "Hardware Daemon" providing all of the hardware
related predefined variables and "UD4" used for updates of the GUI definition on the
display.
If considering to add your own process to communicate with PClient please contact our
support team and expect to include some C++ libraries for the communication between
the two in your program.
If PClient itself is the owner of a variable generally the same rules apply as for other
owners. PClient has no built-in knowledge about which values of a variable are
acceptable and which are not - except for the absolute minimum and maximum values.
Therefore PClient basically accepts and confirms all write requests to its variables.
Since PClient is active as long as the GUI is shown, PClient variables are valid if they
ever got a valid value.
Which Owner should be assigned to a variable?
Generally the idea is to assign the variable to the owner knowing the system's limits and
measuring its state. This means that e.g. engine coolant temperature should be owned
by engine ECU.
On the other hand there may be some setpoints and GUI internal variables which should
be owned by PClient.
A decision has to be made if a variable has to be considered a measured value as well
as a setpoint.
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