Elmo Gold Maestro G-MAS, Software User Manual

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G ‐ MAS – Gold Maestro Software User’s Manual Software User Manual
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Figure 2: MachineSequences() function
Now we have a program that is “slowly” looping in a background –an almost idle loop, while a timer
function, MachineSequencesTimer() is triggered and executed each TIMER_CYCLE ms (20ms in our
example), to execute the States Machine.
Let’s investigate the MachineSequencesTimer() function in ‐ depth.
3.5.3. The MachineSequencesTimer() function
Figure 3 presents the general structure of a typical MachineSequencesTimer() function.
Why "general"? Because it does not present the details of the States Machines. This will be
presented only later. First, understand the general structure of the MachineSequencesTimer()
function.
Initially, upon a Timer event (each TIMER_CYCLE ms, as initialized above), the
MachineSequencesTimer() function is triggered. Its first action is to call the ReadAllInputData()
function.
The ReadAllInputData() function is an application dependent function. Its task is to read all inputs
that may be necessary for the States Machines and to copy them into variables that are not
accessible by the "external world".
This will ensure that all the States Machines code, as executed during this timer event, will use the
same values of input variables.
Why this is needed?
As the timer event is not necessarily synchronized with "external world" operations, a host, for
example, can access the MODBUS memory and modify one of the registers that are used by the
States Machines code. Similarly, the G ‐ MAS core can obtain a new reading of e.g. drive's speed over
the device network. As such "input data" can be changed by the external world during the
MachineSequencesTimer() execution, creating inconsistent operation of the code's flow. It is
necessary first to copy all necessary values into "mirror variables" and only then start to use these
mirror variables, which will remain unchanged until the next timer event.
This is exactly the task of the ReadAllInputData() function. Depending on the application, it should
access all necessary variables (of the MODBUS memory, from the G ‐ MAS firmware core, etc.) and
copy them into "mirror variables".
It is extremely important to read and create a copy of all necessary "external world" variables at the
beginning of MachineSequencesTimer() – using the ReadAllInputData() function – and to use only
these copies, or mirrors, during the States Machines code. This will avoid difficulties in
synchronization and inconsistent code behavior.