PLC Proxy Device Coordinates Memory Access Priority
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Real-time systems face challenges when integrated with virtualization due to differing time expectations and conflicting data access operations, particularly with programmable logic controllers (PLCs) having unpredictable memory access times, which can lead to synchronization issues and violations of exacting real-time demands.
Innovation Solution
A computation apparatus with a proxy device that coordinates memory access to ensure the programmable logic controller has priority, using a proxy device to manage access requests from both the PLC and subordinate systems like virtual machines, ensuring reliable access within a predefined period and implementing a 'roll-back' method to maintain real-time operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a programmable logic controller (PLC) cooperates with a virtual machine system, then resource utilization is improved and processor time is reduced, but memory access time becomes unpredictable and real-time demands are violated
Solution Approach 1:
A proxy device is introduced as an intermediary between the virtual machine system and the PLC memory. The proxy coordinates memory access requests from the virtual machine, ensuring that PLC memory access operations maintain their timing predictability while still allowing virtual machine access to shared data. This mediator resolves the conflict between resource sharing and real-time performance.
2Reliability
If synchronization mechanisms (semaphores, Mutex) are used to coordinate memory access, then data consistency is improved, but access operations become conflicting and real-time demands are violated
Solution Approach 1:
The synchronization function is extracted from the PLC system and implemented in the proxy device instead. The proxy handles coordination of virtual machine access to PLC memory, isolating the synchronization logic from the real-time PLC operations. This allows the PLC to access memory without being blocked by synchronization mechanisms, maintaining real-time performance while ensuring data consistency through the proxy's coordination.
Data Source
AI summary
A programmable logic controller (PLC) with changing memory access times is intended to interact with a subordinate system, i.e., a discontinuous virtualized system, wherein a computation apparatus is provided, in which the PLC is implemented and in which the system that is subordinate to the PLC with respect to an operation to access the memory access is implemented. A memory to which a component of the PLC has access is integrated in the PLC. Also implemented in the computation apparatus is a proxy device that coordinates access to the memory of the PLC by the subordinate system such that simultaneous access by the component of the PLC has priority over access by the subordinate system and it is thus possible to ensure that the PLC always complies with a predefined cycle time of the PLC.