1. EE 472 – Embedded Systems
Dr. Shwetak Patel

2. Agenda Lab 2 overview Operating System Tasks Threads Interrupts
Scheduling 2
Shwetak N. Patel - EE 472

3. Embedded Software Execute a specialized program Perform calculations
Access memory
Communicate with external devices 3
Shwetak N. Patel - EE 472

4. Operating System Makes your life easier! Executes your code
Does memory management
Handles I/O and communications within your program 4
Shwetak N. Patel - EE 472

5. An Embedded Program Task Unit of code Think of it as a C function 5
Shwetak N. Patel - EE 472

6. Scheduler
Part of the OS that execute the tasks so they all get a turn.
Make decisions about when to run the tasks 6
Shwetak N. Patel - EE 472

7. Types of Tasks Periodic Found in hard-real time applications
Three attributes:
P, Period
C, Computing Resources
D, Deadline 7
Shwetak N. Patel - EE 472

8. Types of Tasks Intermittent Found in all applications Two attributes:
C, Computing Resources
D, Deadline 8
Shwetak N. Patel - EE 472

9. Types of Tasks Background Soft-real time Lower priority One attribute:
C, Computing Resources 9
Shwetak N. Patel - EE 472

10. Types of Tasks Complex Continuous need for CPU
Frequent requests for I/O
Wait for user input 10
Shwetak N. Patel - EE 472

11. Multitasking Multiple processes running in a program 11
Shwetak N. Patel - EE 472

12. Task States Ready Running Waiting (for something other than CPU)
Preempted or blocked
Inactive/Terminated 12
Shwetak N. Patel - EE 472

13. Context Switch A new task is switched in
Need to save the current context
Code
Data
Registers
Resources (memory, io, etc) 13
Shwetak N. Patel - EE 472

14. Threads Smaller unit of computation Owned by a process
Like pieces within a process
Smaller context 14
Shwetak N. Patel - EE 472

15. Threads
Example
Web server 15
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16. Processes and Threads 16
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17. Real-Time Operating System
Deterministic
Rigid time constraints 17
Shwetak N. Patel - EE 472

18. Scheduler Responsible for dispatching/executing tasks
When and how long to run a task
Scheduling strategies
Time sharing
Priorities 18
Shwetak N. Patel - EE 472

19. Representing a Task Task Control Block (TCB)
Contains information about a task
Think of a struct 19
Shwetak N. Patel - EE 472

20. TCB

21. TCB

22. Task or Job Queue
Holds a collection of TCBs when a task enters a system
Array or list of structs 22
Shwetak N. Patel - EE 472

25. Problems with this approach?

26. Problems with this approach?
Wastes time waiting for input
Need to use interrupts

27. Interrupts External event Causes a context switch
Each interrupt has a specific ID
Interrupts are found in a interrupt vector table

28. Interrupt Vector Table
Interrupt number
Interrupt service routines (ISR)

29. Questions? Next time: Scheduling algorithms
Print out scheduling worksheet
Shwetak N. Patel - EE 472