1. Chapter 11: Message Queue Management

2. Functions OSQCreate() OSQDel() OSQFlush() OSQPend() OSQAccept()
Flushing a queue
OSQPend()
OSQAccept()
OSQPost()
Sending a message to a queue (FIFO)
OSQPostFront()
Sending a message to a queue (LIFO)
OSQPostOpt()
Sending a message to a queue (LIFO or FIFO)
OSQQuery()

3. Tasks, ISR, and a Message Queue

4. Data Structures for a Message Queue

5. Queue Control Block (QCB)

6. Fields in the QCB
.OSQPtr: links free QCB .OSQStart: point to the start of the queue .OSQEnd: point to the location past the end of the queue .OSQIn: point to location where the next message will be inserted. .OSQOut: point to the next message to be extracted from the queue .OSQSize: Contains the size of the message storage area. .OSQEntries: contains the number of entries in the queue

7. List of Free Queue Control Blocks (QCB)

8. A circular buffer

9. OSQCreate()

10. OSQCreate()

11. OSQDel() Case 1: OS_DEL_NO_PEND Case 2: OS_DEL_ALWAYS
Return queue control block
Return event control block
Case 2: OS_DEL_ALWAYS
Ready all waiting tasks
Schedule

12. OSQDel()

13. OSQDel()

14. OSQDel()

15. OSQPend()

16. OSQPend()

17. OSQPost() Case 1: at least one task pending on the queue
Ready the highest priority task
Case 2: otherwise
The queue is full  return (non-blocking)
The queue is not full  insert the message

18. OSQPost()

19. OSQPostFront() Case 1: at least one task pending on the queue
Ready the highest priority task
Case 2: otherwise
The queue is full  return (non-blocking)
The queue is not full  insert the message

20. OSQPostFront()

21. OSQPostOpt()
pevent: is a pointer to the event control block associated with the desired queue
msg: is a pointer to the message to send
opt
OS_POST_OPT_NONE: identical to OSQPost()
OS_POST_OPT_FRONT: identical to OSQPostFront()
OS_POST_OPT_BROADCAST: identical to OSQPost() but will broadcast 'msg' to ALL waiting tasks
OS_POST_OPT_FRONT + OS_POST_OPT_BROADCAST: is identical to OSQPostFront() except that will broadcast 'msg' to ALL waiting tasks

22. OSQPostOpt()

23. OSQPostOpt()

24. OSQFlush()
Reset the variables – .OSQIn, .OSQOut and .OSQEntries

25. OSQFlush()