1. TrueTime

2. TrueTime 2.0 http://www.control.lth.se/truetime/ Reference Manual link

3. Communication Network
TrueTime is a Matlab/Simulink Event-based simulator for real-time control system.
It is used for the simulation of Networked Control System (NCS).
In NCS, actuators, sensors and controllers are interconnected by a communication network.
Process
Actuator
Sensor
Communication Network
Controller

4. TrueTime capabilities:
Investigate the true, timely behavior of time or event-triggered control loops affected by real-time scheduling and networking
Experiment with novel real-time scheduling techniques, including feedback scheduling
Investigate the performance of various wired or wireless MAC protocols
Simulate complex scenarios involving battery-powered mobile robots communicating over a wireless network

5. Components

6. Computation component
Simulates and event-based real- time kernel.
Executes user-defined tasks and interrupt handler (C or M-files)
Arbitrary user-defined scheduling policies
Supports external interrupts and timers
Code structured into code segments

7. Init Each kernel block must have an initialization script
The purposes of the initialization script are:
Specify the number of I/O
Define a scheduling policy
Creating tasks
Creating interrupts handlers
Pre-defined priority functions exist for scheduling policies:
fixed-priority
rate-monotonic
deadline-monotonic
earliest-deadline-first scheduling

8. Example Initialize the kernel, specifying the scheduling policy
Create a periodic task
Create an aperiodic task
Attach an aperiodic task or interrupt handler to a network interface

9. Tasks Tasks are used to model the execution of user code
The release of task instances (jobs) may be periodic or aperiodic
For periodic tasks, the jobs are created by an internal periodic timer
For aperiodic tasks, the jobs must be created by the user (e.g., in response to interrupts)

10. Task code is represented by a code function in the format: [exectime,data] = function mycode(segment,data) The data input/output argument represents the local memory of the task The segment input argument represents the program counter The exectime output argument represents the execution time of the current code segment

11. All statements in a segment are executed sequentially, non- preemptively, and in zero simulation time Only the delay can be preempted by other tasks No local variables are saved between segments

12. The name of the initialization script
An optional argument to the initialization script
Number of local Inputs and Outputs
Number of external triggers for the kernel task
Number of the node (must be unique)
A constant time offset and time drift from the nominal time.

13. Communication component
Network Block
Ethernet
CAN
TDMA
FDMA
Round Robin
Switched Ethernet
FlexRay
PROFINET
Wireless Network Block
802.11b WLAN
ZigBee

14. Modelling wired networks
Models the medium access delay and the transmission delay.
No built-in support for network and transport layer protocols

15. Modelling wireless network
Used in a similar way as the wired network block
Supports two common MAC layer policies:
802.11b/g (WLAN)
(ZigBee)
Variable network parameters x and y inputs for node locations
Generates a transmission schedule

16. The number assigned to the network block.
The number of nodes connected to the network.
The speed of the network.
The minimum frame size
The probability that a network message is lost during transmission

17. Example Networked

18. Networked control of a DC-Servo
Controller Task
Dummy Task
Sensor Task
Actuator Task
Interfering Task
Controller
Sensor / Actuator
Interfering Node
CSMA/CD
80 kbps

19. Networked Control Loop

20. Step Response
Step Response
Control Signal

21. Network Schedule Control Node Sensor/Actuator Node Interfering Node
High → Sending
Medium → Waiting
Low → Idle

22. CPU Schedule Actuator Task Sensor Task High → Running Medium → Ready
Low → Idle