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Embedded Systems Lab 3 - HS 201928.10.2019Andreas Biri, Matthias Meyer
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 1
Goals
Introduce a real-time operating system (RTOS)
Learn what tasks are and how to create them
Get to know task states and priorities
Implement inter-task communication using queues
Learn how to handle critical sections
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 2
Tasks
Running
Ready BlockedSuspended
Not Running
vTaskSuspend() Blocking API function call
Event
vTaskResume()
vTaskSuspend()
vTaskSuspend()
OS allows splitting up theapplication into independent tasks
Tasks can be individually put intonew states depending on theirbehaviour
Priority signals scheduler whichtask to prefer
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 3
Critical sections
Pre-emption: Tasks can be interrupted by other events
Time slicing: Scheduler shares processing time between tasks
However, this might stop time-critical interactions (e.g. withperipherals, such as when reading from a sensor)
Mutex: Guarantees exclusive access to a shared resource
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 4
Related chapters from the lecture
Ch. 5: Embedded Operating Systems
Ch. 5: FreeRTOS Task Management → Task 1Task functionsCreation of tasksTask handles and deletion at runtime
Ch. 7: Resource Sharing → Task 2Example of shared resource conflictMutual exclusion
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 5
Related chapters from the lecture
Ch. 5: FreeRTOS Timers and FreeRTOS Task States → Task 2DelayBlocked, Ready, Running StatesEvents
Ch. 7: Communication and Synchronization → Task 3Communication between tasksQueues
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 6
FreeRTOS
The lab is self-contained but cannot cover everything aboutFreeRTOS
Supplementary material can help to understand the content andgo beyond
https://www.freertos.org/FreeRTOS Reference Manual v9.0.0.Book: Mastering the FreeRTOS Real Time Kernel
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 7
Questions?
Andreas BiriETZ G75+41 44 632 08 [email protected]
Matthias MeyerETZ G81+41 44 632 04 [email protected]
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Andreas Biri, Matthias Meyer 28.10.2019 8
Lab 3
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory
Andreas Biri, Matthias Meyer 28.10.2019 Page 1 of 1
