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8.6. Implementation
execution
global
∆t ∆t ∆t ∆t ∆t
local
0 t
t e
∆t
0
1T s 2T s 3T s 4T s 5T s
Figure 8.22.: Example of global and local execution drift
t
pp. 457-504] of a real-time system.
8.6.3. Control Flow Implementation
As the execution of CControlFlow objects is driven by the CDataFlow objects and CControlFlow
objects are always a part of CDataFlow objects, their implementation is not relevant for
a detailed discussion here. While the CDataFlow instances handle the transition to new
CEVCState objects by their m_TransitionStack, CControlFlow must take care of transition
between its CState objects by itself. In contrast to the transition between CEVCState instances,
the evaluation of transition between CState objects is done in the currently executed CState
object and not in the parent CControlFlow instance. This simplification can be done because
a control flow cannot be executed in parallel as independent data flow.
Thus, a CState object executes all CFunctionBlock objects m_FunctionBlocks and afterwards
evaluates its transition stack m_TransitionStack, which is implemented in Listing D.4 in
Appendix D.
8.6.4. EVC State Machine Implementation
Since the core functionality of the openETCS domain framework or rather the execution of
the currently active data flows is located in CDataFlow, the transition between EVC Modes
and switching to ETCS Application Levels is mostly implemented in CDataFlow. Also, the
CEVCStateMachine::Start() should be non-blocking according to the behavioural design
in Section 8.4. Hence, the execution of CEVCState must be done in a separated thread
that is created and started by that method. The thread is implemented in a method of
CEVCStateMachine:
void CEVCStateMachine : : StateThread ( ) throw ( )
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