The Time-Triggered Model of Computation Lior Zimet

1. The Time-Triggered Model of ComputationLior Zimet

2. Outline • Introduction • Temporal accuracy of information • Layering versus Partitioning • The TT model of computation • The client-server model versus the TT model • Conclusions

3. Introduction • Hard real-time systems cannot tolerate violation of computational deadline • More difficult to understand and design and therefore need a reduced representation of the system model • Client-server models are used for distributed systems, but they have no notion of time. • TT-model is based on the time of the real-time information • TT- model objective is to provide the high level description of large real-time system, focusing on temporal data accuracy

4. Temporal accuracy of information • Real-time data losses validity as time progress • Real-time Entity–a significant set of state values of a controlled object that were captured in time. • Observation– captures the information from the RT entity Observation = <Name, tobs, Value> • Real-time Image–current picture of an RT entity • Temporal Accuracy–relationship between the RT image and RT entity history

5. Temporal accuracy of information • RT image lag behind RT entity because of the transmission time from the observing node to the receiving node • The delay between the observation of entity and the use of image causes an error: • State estimation –estimatesthe point in time where the value of RT image is causing an action in the environment • State estimation can be used to bring the RT image into better agreement with RT entity

6. Layering versus partitioning • Two kinds of system structuring to reduce complexity: • Successive hierarchically-ordered layers • Partitioning of a large system into nearly independent subsystems with their own resources and interfaces • Two steps to structure a system: • Partition into nearly decomposable subsystems of high inner connectivity and low external connectivity • Each subsystem internally can be structured according to the layering technique

7. Layering versus partitioning • Functional partitioning of the hardware can lead to number of advantages: • Reduced need for resource multiplexing • Easier to observe resource failure and errors • Implementation complexity of a partition can be hidden behind it’s interface specification. • Reusability of partitions

8. The TT model of computation • The TT model is based on partitioning of a the large distributed system to autonomous subsystems with four basic blocks: • Interface • Communication system • Host computer • Transducer Air traffic control

9. The TT model of computation - Interface • Contains shared memory element between two subsystems • Temporal firewall describes the properties of the I/F: • Phase-insensitive • Phase-sensitive

10. The TT model of computation - Interface • Stable properties: • Names and syntactic of data items • Point in time when data items are accessed • Temporal accuracy of data items • The producer is obligated to provide temporal accurate RT images • The consumer is obligated to sample the information in a sampling rate that will ensure temporal accuracy

11. The TT model of computation - continue • The communication systemconnects interfaces within a priori known deterministic time bounds • The host computer reads and writes the data from the interfaces in a known a priori time instants • The Transducer models the input/output of the system. It makes the translationfrom the environment to RT image and vice versa

12. Client-Server versus TT model

13. Client-server versus TT model

14. Conclusions • The TT model specifies interface and communication of subsystems of a large distributed hard real-time system • Separates cleanly the design of the interaction among components from the design of the components themselves. • Supports constructive implementation of large real-time systems • Requires the availability of the timedtriggered communication implementation.