1. Introduction to uC/OS-II

2. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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3. Real-Time Systems Concepts
Multitasking
Kernel
Scheduling
Mutual Exclusion
Message Passing
Interrupt
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4. Foreground/Background Systems
Interrupt Level
Task Level
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5. Multitasking Multitasking Related issues
A process of scheduling and switching CPU between several tasks.
Related issues
Context Switch (Task Switch)
Resource Sharing
Critical Section
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6. Multitasking
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7. Task
A task, or called a thread, a simple program that thinks it has the CPU all to itself.
Each task is assigned a priority, its own set of CPU registers, and its own stack area .
Each task typically is an infinite loop that can be in any one of five states.
Ready, Running, Waiting, ISR, Dormant
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8. Task States
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9. Non-Preemptive Kernel
Kernel is the part of a multitasking system responsible for the management of tasks.
Context switching is the fundamental service of a kernel.
Non-Preemptive Kernel
v.s.
Preemptive Kernel
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10. Non-Preemptive Kernel
Cooperative multitasking
A non-preemptive kernel allows each task to run until it voluntarily gives up control of the CPU.
An ISR can make a higher priority task ready to run, but the ISR always returns to the interrupted task.
Linux 2.4 is non-preemptive.
Linux 2.6 is preemptive.
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11. Non-Preemptive Kernel
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12. Preemptive Kernel
A preemptive kernel always executes the highest priority task that is ready to run.
µC/OS-II and most commercial real-time kernels are preemptive.
Much better response time.
Should not use non-reentrant functions, unless the functions are mutual exclusive.
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13. Preemptive Kernel
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14. Function Reentrancy
A reentrant function is a function that can be used by more than one task without fear of data corruption.
Reentrant functions either use local variables or protected global variables.
OS_ENTER_CRITICAL()
OS_EXIT_CRITICAL()
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15. Function Reentrancy Non-Reentrant Function Reentrant Function
static int Temp;
void swap(int *x, int *y)
{ Temp = *x; *x = *y; *y = Temp; }
Reentrant Function
void strcpy(char *dest, char *src) {
while (*dest++ = *src++) { ; } *dest = NULL; }
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16. Scheduling Round-Robin Scheduling Task Priority Assignment
Tasks executed sequentially
Task Priority Assignment
Static priority
Rate Monotonic (RM)
Dynamic priority
Earliest-Deadline First (EDF)
Time-Derived Scheduling
Pinwheel
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17. Round-Robin Kernel gives control to next task if the current task
has no work to do
completes
reaches the end of time-slice
Not supported in uC/OS-II
O(1) priority preemptive scheduling
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18. Priority Inversion Problem
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19. Priority Inheritance
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20. Mutual Exclusion Protected shared data of processes.
Exclusive access implementation
Disabling and enabling interrupts
Test-and-Set
Disabling and enabling scheduler
Semaphores
Simple Semaphore
Counting Semaphore
Deadlock – set timeout for a semaphore
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21. Using Semaphore
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22. Synchronization
Synchronization mechanism is used between tasks or task to ISR.
Unilateral rendezvous
Bilateral rendezvous
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23. Unilateral rendezvous
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24. Bilateral rendezvous
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25. Event Flags
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26. Message Passing Intertask Communication
Using global variables or sending messages
Only communicate to ISR through global variables
Tasks are not aware when the global variables is changed unless task polls the content.
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27. Message Mailboxes
A Message Mailbox, also called a message exchange, is typically a pointer size variable.
Operations
Initial
POST
PEND
necessary to wait for the message being deposited
ACCEPT
Acknowledgement
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28. Message Queues
A message queue is used to send one or more messages to a task.
A message queue is an array of message mailboxes.
Generally, FIFO is used.
µC/OS-II allows a task to get messages Last-In-First-Out (LIFO).
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29. Interrupt
An interrupt is a hardware mechanism used to inform the CPU that an asynchronous event has occurred.
Interrupt Latency
Interrupt Response
Interrupt Recovery
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30. Interrupt Nesting
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31. Interrupt Latency Disabling interrupts affects interrupt latency.
All real-time systems disable interrupts to manipulate critical sections of code.
Re-enable interrupts when the critical section has executed.
Interrupt latency = Maximum time to disable interrupts + Time to start the first instruction in ISR.
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32. Interrupt Response
Interrupt Response means time between the reception of the interrupt and the start of the user code which will handle the interrupt.
Interrupt response = Interrupt latency + Time to save CPU context
The worst case for interrupt response is adopted.
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33. Interrupt Recovery
Interrupt recovery is defined as the time required for the processor to return to the interrupted code.
Interrupt recovery = Time to determine if a high priority task is ready + Time to restore the CPU context of the highest priority task + time of executing return-from-interrupt.
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34. Non-preemptive Kernel
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35. Preemptive Kernel
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36. Non-Maskable Interrupts (NMIs)
Service the most important time-critical ISR
Can not be disabled
Interrupt latency = Time to execution the longest instruction + Time to start execution the NMI ISR
Interrupt response = Interrupt latency + Time to save CPU context
Interrupt recovery = Time to restore CPU context + time of executing return-from-interrupt
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37. Clock Tick A periodical interrupt Be viewed as heartbeat
Application specific and is generally between 10ms and 200ms
Faster timer causes higher overhead
Delay problem should be considered in real-time kernel.
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38. Delaying a Task for 1 Tick
Tick Interrupt
Tick ISR
All higher priority tasks
Delayed Task t1 t2 t3
20 mS
(6 mS)
(19 mS)
(27 mS)
Call to delay 1 tick (20 mS)
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39. Clock Tick Solve the problem
Increase the clock rate of your microprocessor.
Increase the time between tick interrupts.
Rearrange task priorities.
Avoid using floating-point math.
Get a compiler that performs better code optimization.
Write time-critical code in assembly language.
If possible, upgrade to a faster microprocessor in the same family.
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40. Memory Requirement Be careful to avoid large RAM requirement
Large local arrays
Nested/Recursive function
Interrupt nesting
Stack used by libraries
Too many function arguments
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41. Real-Time Kernels
Real-time OS allows real-time application to be designed and expanded easily.
The use of an RTOS simplifies the design process by splitting the application into separate tasks.
Real-time kernel requires more ROM/RAM and 2 to 4 percent overhead.
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42. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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43. Kernel Structure Task Control Blocks Ready List Task Scheduling
Interrupt under uC/OS-II
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44. Critical Sections Archive this by disabling interrupt OS_CPU.H
OS_ENTER_CRITICAL()
OS_EXIT_CRITICAL()
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45. Tasks Up to 64 tasks Two tasks for system use(idle and statistic)
Priorities 0, 1, 2, 3, OS_LOWEST_PRIO-3, OS_LOWEST_PRIO-2, OS_LOWEST_PRIO-1, OS_LOWEST_PRIO for future use
The lower the priority number, the higher the priority of the task.
The task priority is also the task identifier.
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46. Task States
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47. Task Control Blocks 06:10 /27 typedef struct os_tcb {
OS_STK *OSTCBStkPtr;
 #if OS_TASK_CREATE_EXT_EN
void *OSTCBExtPtr;
OS_STK *OSTCBStkBottom;
INT32U OSTCBStkSize;
INT16U OSTCBOpt;
INT16U OSTCBId;
#endif
  struct os_tcb *OSTCBNext;
struct os_tcb *OSTCBPrev;
#if (OS_Q_EN && (OS_MAX_QS >= 2)) || OS_MBOX_EN || OS_SEM_EN
OS_EVENT *OSTCBEventPtr;
 #if (OS_Q_EN && (OS_MAX_QS >= 2)) || OS_MBOX_EN
void *OSTCBMsg;
INT16U OSTCBDly;
INT8U OSTCBStat;
INT8U OSTCBPrio;
INT8U OSTCBX;
INT8U OSTCBY;
INT8U OSTCBBitX;
INT8U OSTCBBitY;
#if OS_TASK_DEL_EN
BOOLEAN OSTCBDelReq;
} OS_TCB;
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48. OS_TCB Lists TCBs store in OSTCBTbl[]
All TCBs are initialized and linked when uC/OS-II is initialized
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49. Ready List
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50. OSRdyGrp and OSRdyTbl[]
Bit 0 in OSRdyGrp is 1 when any bit in OSRdyTbl[0] is 1.
Bit 1 in OSRdyGrp is 1 when any bit in OSRdyTbl[1] is 1.
Bit 2 in OSRdyGrp is 1 when any bit in OSRdyTbl[2] is 1.
Bit 3 in OSRdyGrp is 1 when any bit in OSRdyTbl[3] is 1.
Bit 4 in OSRdyGrp is 1 when any bit in OSRdyTbl[4] is 1.
Bit 5 in OSRdyGrp is 1 when any bit in OSRdyTbl[5] is 1.
Bit 6 in OSRdyGrp is 1 when any bit in OSRdyTbl[6] is 1.
Bit 7 in OSRdyGrp is 1 when any bit in OSRdyTbl[7] is 1.
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51. Making a Task Ready to Run
OSRdyGrp |= OSMapTbl[prio >> 3];
OSRdyTbl[prio >> 3] |= OSMapTbl[prio & 0x07];
Index
Bit mask (Binary) 1 2 3 4 5 6 7
Task’s Priority Y X
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52. Removing a Task from the Ready List
if ((OSRdyTbl[prio >> 3] &= ~OSMapTbl[prio & 0x07]) == 0)
OSRdyGrp &= ~OSMapTbl[prio >> 3];
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53. Finding the Highest Priority Task
OSUnMapTbl[] …
y = OSUnMapTbl[OSRdyGrp];
x = OSUnMapTbl[OSRdyTbl[y]];
prio = (y << 3) + x;
INT8U const OSUnMapTbl[] = {
0, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0 };
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54. Task Scheduler void OSSched (void) { INT8U y; OS_ENTER_CRITICAL();
if ((OSLockNesting | OSIntNesting) == 0) { (1)
y = OSUnMapTbl[OSRdyGrp]; (2)
OSPrioHighRdy = (INT8U)((y << 3) + OSUnMapTbl[OSRdyTbl[y]]); (2)
if (OSPrioHighRdy != OSPrioCur) { (3)
OSTCBHighRdy = OSTCBPrioTbl[OSPrioHighRdy]; (4)
OSCtxSwCtr++; (5)
OS_TASK_SW(); (6) }
OS_EXIT_CRITICAL();
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55. Locking The Scheduler
void OSSchedLock (void) { if (OSRunning == TRUE) { OS_ENTER_CRITICAL(); OSLockNesting++; OS_EXIT_CRITICAL(); } }
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56. Unlocking The Scheduler
void OSSchedUnlock (void)
{ if (OSRunning == TRUE) { OS_ENTER_CRITICAL(); if (OSLockNesting > 0) { OSLockNesting--; if ((OSLockNesting | OSIntNesting) == 0) { (1) OS_EXIT_CRITICAL(); OSSched(); (2) } else { OS_EXIT_CRITICAL(); } } else { OS_EXIT_CRITICAL(); } } }
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57. Idle Task OSTaskIdle() Lowest priority, OS_LOWEST_PRIO
void OSTaskIdle (void *pdata) { pdata = pdata; for (;;) { OS_ENTER_CRITICAL(); OSIdleCtr++; OS_EXIT_CRITICAL(); } }
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58. Statistics Task
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59. Initializing the Statistic Task
void main (void) { OSInit(); /* Initialize uC/OS-II (1)*/ /* Install uC/OS-II's context switch vector */ /* Create your startup task (for sake of discussion, TaskStart()) (2)*/ OSStart(); /* Start multitasking (3)*/ }
void TaskStart (void *pdata) { /* Install and initialize µC/OS-II’s ticker (4)*/ OSStatInit(); /* Initialize statistics task (5)*/ /* Create your application task(s) */ for (;;) { /* Code for TaskStart() goes here! */ } }
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60. Initializing the Statistic Task
void OSStatInit (void) {
OSTimeDly(2);
OS_ENTER_CRITICAL();
OSIdleCtr = 0L;
OS_EXIT_CRITICAL();
OSTimeDly(OS_TICKS_PER_SEC);
OSIdleCtrMax = OSIdleCtr;
OSStatRdy = TRUE; }
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61. Statistics Task 06:10 /27 void OSTaskStat (void *pdata) { INT32U run;
INT8S usage;
pdata = pdata;
while (OSStatRdy == FALSE) { (1)
OSTimeDly(2 * OS_TICKS_PER_SEC); }
for (;;) {
OS_ENTER_CRITICAL();
OSIdleCtrRun = OSIdleCtr;
run = OSIdleCtr;
OSIdleCtr = 0L;
OS_EXIT_CRITICAL();
if (OSIdleCtrMax > 0L) {
usage = (INT8S)(100L - 100L * run / OSIdleCtrMax); (2)
if (usage > 100) {
OSCPUUsage = 100;
} else if (usage < 0) {
OSCPUUsage = 0;
} else {
OSCPUUsage = usage;
OSTaskStatHook(); (3)
OSTimeDly(OS_TICKS_PER_SEC);
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62. Interrupts under uC/OS-II
Be written in assembly language or C code with in-line assembly.
YourISR: Save all CPU registers; (1) Call OSIntEnter() or, increment OSIntNesting directly; (2) Execute user code to service ISR; (3) Call OSIntExit(); (4) Restore all CPU registers; (5) Execute a return from interrupt instruction;
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63. Servicing an Interrupt
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64. Beginning an ISR
void OSIntEnter (void) { OS_ENTER_CRITICAL(); OSIntNesting++; OS_EXIT_CRITICAL(); }
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65. Leaving an ISR void OSIntExit (void) { OS_ENTER_CRITICAL(); (1)
if ((--OSIntNesting | OSLockNesting) == 0) { (2)
OSIntExitY = OSUnMapTbl[OSRdyGrp]; (3)
OSPrioHighRdy = (INT8U)((OSIntExitY << 3) +
OSUnMapTbl[OSRdyTbl[OSIntExitY]]);
if (OSPrioHighRdy != OSPrioCur) {
OSTCBHighRdy = OSTCBPrioTbl[OSPrioHighRdy];
OSCtxSwCtr++;
OSIntCtxSw(); (4) }
OS_EXIT_CRITICAL();
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66. Pseudo Code for Tick ISR
void OSTickISR(void) { Save processor registers; Call OSIntEnter() or increment OSIntNesting; Call OSTimeTick(); Call OSIntExit(); Restore processor registers; Execute a return from interrupt instruction; }
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67. Service a Tick
void OSTimeTick (void) { OS_TCB *ptcb; OSTimeTickHook(); (1) ptcb = OSTCBList; (2) while (ptcb->OSTCBPrio != OS_IDLE_PRIO) { (3) OS_ENTER_CRITICAL(); if (ptcb->OSTCBDly != 0) { if (--ptcb->OSTCBDly == 0) { if (!(ptcb->OSTCBStat & OS_STAT_SUSPEND)) { (5) OSRdyGrp |= ptcb->OSTCBBitY; (4) OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX; } else { ptcb->OSTCBDly = 1; } } } ptcb = ptcb->OSTCBNext; OS_EXIT_CRITICAL(); } OS_ENTER_CRITICAL(); (7) OSTime++; (6) OS_EXIT_CRITICAL(); }
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68. uC/OS-II Initialization
Initialize variables and data structures
Create the idle task OSTaskIdle()
Create the statistic task OSTaskStat()
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69. After calling OSInit()
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70. Starting uC/OS-II
void main (void) { OSInit(); /* Initialize uC/OS-II */ Create at least 1 task using either OSTaskCreate() or OSTaskCreateExt(); OSStart(); /* Start multitasking! OSStart() will not return */ }
void OSStart (void) { INT8U y; INT8U x;   if (OSRunning == FALSE) { y = OSUnMapTbl[OSRdyGrp]; x = OSUnMapTbl[OSRdyTbl[y]]; OSPrioHighRdy = (INT8U)((y << 3) + x); OSPrioCur = OSPrioHighRdy; OSTCBHighRdy = OSTCBPrioTbl[OSPrioHighRdy]; (1) OSTCBCur = OSTCBHighRdy; OSStartHighRdy(); (2) } }
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71. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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72. Task Management Task prototype Create a task Task stacks
Stack checking
Delete a task
Change a task’s priority
Suspend a task
Resume a task
Query task information
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73. Task Prototype
void YourTask (void *pdata) { for (;;) { /* USER CODE */ Call one of uC/OS-II’s services: /* USER CODE */ } }
void YourTask (void *pdata) { /* USER CODE */ OSTaskDel(OS_PRIO_SELF); }
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74. OSTaskCreate() Check that the task priority is valid
Check that the task is unique
Set up the task stack
OSTaskStkInit()
Obtain and initialize OS_TCB from TCB pool
OSTCBInit()
Call OSTaskCreateHook() to extend the functionality
Call OSSched() when OSTaskCreate() is called from a task
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75. INT8U OSTaskCreate (void (. task)(void. pd), void. pdata, OS_STK
INT8U OSTaskCreate (void (*task)(void *pd), void *pdata, OS_STK *ptos, INT8U prio) {
void *psp;
INT8U err;
if (prio > OS_LOWEST_PRIO) { (1)
return (OS_PRIO_INVALID); }
OS_ENTER_CRITICAL();
if (OSTCBPrioTbl[prio] == (OS_TCB *)0) { (2)
OSTCBPrioTbl[prio] = (OS_TCB *)1; (3)
OS_EXIT_CRITICAL(); (4)
psp = (void *)OSTaskStkInit(task, pdata, ptos, 0); (5)
err = OSTCBInit(prio, psp, (void *)0, 0, 0, (void *)0, 0); (6)
if (err == OS_NO_ERR) { (7)
OSTaskCtr++; (8)
OSTaskCreateHook(OSTCBPrioTbl[prio]); (9)
OS_EXIT_CRITICAL();
if (OSRunning) { (10)
OSSched(); (11)
} else {
OSTCBPrioTbl[prio] = (OS_TCB *)0; (12)
return (err);
return (OS_PRIO_EXIST);
OSTaskCreate()
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76. OSTaskCreateExt() More flexibility, at the expense of overhead
The first four arguments are the same as OSTaskCreate()
id, assign a unique identifier for the task
pbos, a pointer that can perform stack checking
stk_size, specifies the size of the stack
pext, a pointer to extend the OS_TCB
opt, specifies whether stack checking is performed
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77. OSTaskCreateExt() INT8U OSTaskCreateExt (void (*task)(void *pd),
void *pdata,
OS_STK *ptos,
INT8U prio,
INT16U id,
OS_STK *pbos,
INT32U stk_size,
void *pext,
INT16U opt) {
void *psp;
INT8U err;
INT16U i;
OS_STK *pfill;
if (prio > OS_LOWEST_PRIO) { (1)
return (OS_PRIO_INVALID); }
OS_ENTER_CRITICAL();
if (OSTCBPrioTbl[prio] == (OS_TCB *)0) { (2)
OSTCBPrioTbl[prio] = (OS_TCB *)1; (3)
OS_EXIT_CRITICAL(); (4) …
return (err);
} else {
OS_EXIT_CRITICAL();
return (OS_PRIO_EXIST);
OSTaskCreateExt()
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78. Task Stacks or Using malloc() to allocate stack space
Static OS_STK MyTaskStack[stack_size]; or
OS_STK MyTaskStack[stack_size];
Using malloc() to allocate stack space
OS_STK *pstk;
pstk = (OS_STK *)malloc(stack_size);
if (pstk != (OS_STK *)0) { /* Make sure malloc() had enough space */
Create the task; }
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79. Fragmentation
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80. OSTaskStkChk()
Computes the amount of free stack space by “walking” from the bottom of the stack until a nonzero value is found
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81. Stack Checking
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82. OSTaskDel() Return to the DORMANT state
The code for the task will not be deleted
Procedures
Prevent from deleting and idle task
Prevent from deleting a task from within an ISR
Verify that the task to be deleted does exist
Remove the OS_TCB
Remove the task from ready list or other lists
Set .OSTCBStat to OS_STAT_RDY
Call OSDummy()
Call OSTaskDelHook()
Remove the OS_TCB from priority table
Call OSSched()
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83. OSTaskDelReq()
Tell the task that owns memory buffers or semaphore to delete itself
Procedures
Check the task’s priority
If the task’s priority is OS_PRIO_SELF
Return the flag of OSTCBDelReq
Otherwise
Set OSTCBDelReq of the task to OS_TASK_DEL_REQ
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84. OSTaskDelReq() Example
void RequestorTask (void *pdata) { for (;;) { /* Application code */ if (‘TaskToBeDeleted()’ needs to be deleted) { while (OSTaskDelReq(TASK_TO_DEL_PRIO) != OS_TASK_NOT_EXIST) { OSTimeDly(1); } } /* Application code */ } }
void TaskToBeDeleted (void *pdata) { for (;;) { /* Application code */ if (OSTaskDelReq(OS_PRIO_SELF) == OS_TASK_DEL_REQ) { Release any owned resources; De-allocate any dynamic memory; OSTaskDel(OS_PRIO_SELF); } else { /* Application code */ } } }
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85. OSTaskChangePrio() Cannot change the priority of any idle task
Procedures
Reserve the new priority by OSTCBPrioTbl[newprio] = (OS_TCB *) 1;
Remove the task from the priority table
Insert the task into new location of the priority table
Change the OS_TCB of the task
Call OSSched()
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86. OSTaskSuspend() Procedures Check the input priority
Remove the task from the ready list
Set the OS_STAT_SUSPEND flag in OS_TCB
Call OSSched()
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87. OSTaskResume() Procedures Check the input priority
Clear the OS_STAT_SUSPEND bit in the OSTCBStat field
Set OSTCBDly to 0
Call OSSched()
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88. OSTaskQuery() INT8U OSTaskQuery (INT8U prio, OS_TCB *pdata) {
OS_TCB *ptcb;
if (prio > OS_LOWEST_PRIO && prio != OS_PRIO_SELF) { (1)
return (OS_PRIO_INVALID); }
OS_ENTER_CRITICAL();
if (prio == OS_PRIO_SELF) { (2)
prio = OSTCBCur->OSTCBPrio;
if ((ptcb = OSTCBPrioTbl[prio]) == (OS_TCB *)0) { (3)
OS_EXIT_CRITICAL();
return (OS_PRIO_ERR);
*pdata = *ptcb; (4)
return (OS_NO_ERR);
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89. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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90. Time Management OSTimeDly() OSTimeDlyHMSM() OSTimeDlyResume()
OSTimeGet()
OSTimeSet()
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91. OSTimeDly() void OSTimeDly (INT16U ticks) { if (ticks > 0) {
if ((OSRdyTbl[OSTCBCur->OSTCBY] &= ~OSTCBCur->OSTCBBitX) == 0) {
OSRdyGrp &= ~OSTCBCur->OSTCBBitY; }
OSTCBCur->OSTCBDly = ticks;
OSSched(); } }
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92. OSTimeDlyHMSM()
INT8U OSTimeDlyHMSM (INT8U hours, INT8U minutes, INT8U seconds, INT16U milli) { {
INT32U ticks;
INT16U loops;
if (hours > 0 || minutes > 0 || seconds > 0 || milli > 0) {
if (minutes > 59) {
return (OS_TIME_INVALID_MINUTES); }
if (seconds > 59) {
return (OS_TIME_INVALID_SECONDS);
if (milli > 999) {
return (OS_TIME_INVALID_MILLI);
ticks = (INT32U)hours * 3600L * OS_TICKS_PER_SEC
+ (INT32U)minutes * 60L * OS_TICKS_PER_SEC
+ (INT32U)seconds) * OS_TICKS_PER_SEC
+ OS_TICKS_PER_SEC * ((INT32U)milli + 500L / OS_TICKS_PER_SEC) / 1000L;
loops = ticks / 65536L;
ticks = ticks % 65536L;
OSTimeDly(ticks);
while (loops > 0) {
OSTimeDly(32768);
loops--; }
return (OS_NO_ERR);
} else { return (OS_TIME_ZERO_DLY); }
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93. OSTimeDlyResume() INT8U OSTimeDlyResume (INT8U prio) {
ptcb = (OS_TCB *)OSTCBPrioTbl[prio];
if (ptcb != (OS_TCB *)0) {
if (ptcb->OSTCBDly != 0) {
ptcb->OSTCBDly = 0;
if (!(ptcb->OSTCBStat & OS_STAT_SUSPEND)) {
OSRdyGrp |= ptcb->OSTCBBitY;
OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
OSSched(); }
return (OS_NO_ERR);
} else { return (OS_TIME_NOT_DLY); }
} else { return (OS_TASK_NOT_EXIST); } }
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94. OSTimeGet() & OSTimeSet()
INT32U OSTimeGet (void) {
ticks = OSTime;
return (ticks); }
void OSTimeSet (INT32U ticks) {
OSTime = ticks;
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95. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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96. Intertask Communication & Synchronization
OS_ENTER_CRITICAL() OS_EXIT_CRITICAL()
OSSchedLock() OSSchedUnlock()
Semaphore Message mailbox Message queue
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97. OS_ENTER_CRITICAL() & OS_EXIT_CRITICAL()
#define OS_CRITICAL_METHOD 2
#if OS_CRITICAL_METHOD == 1
#define OS_ENTER_CRITICAL() asm CLI
#define OS_EXIT_CRITICAL() asm STI
#endif
#if OS_CRITICAL_METHOD == 2
#define OS_ENTER_CRITICAL() asm {PUSHF; CLI}
#define OS_EXIT_CRITICAL() asm POPF
CLI …
STI
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98. Linux Example /* include/asm-i386/system.h */
/* interrupt control.. */
#define __save_flags(x) __asm__ __volatile__("pushfl ; popl %0":"=g" (x):)
#define __restore_flags(x)
__asm__ __volatile__("pushl %0; popfl": /* no output */ :"g" (x):"memory", "cc")
#define __cli() __asm__ __volatile__("cli": : :"memory")
#define __sti() __asm__ __volatile__("sti": : :"memory")
/* For spinlocks etc */
#define local_irq_save(x)
__asm__ __volatile__("pushfl; popl %0; cli":"=g" (x): :"memory")
#define local_irq_restore(x) __restore_flags(x)
#define local_irq_disable() __cli()
#define local_irq_enable() __sti()
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99. Locking and Unlocking the Scheduler
void OSSchedLock (void) {
if (OSRunning == TRUE) {
OSLockNesting++; } }
void OSSchedUnlock (void) {
if (OSLockNesting > 0) {
OSLockNesting--;
if ((OSLockNesting | OSIntNesting) == 0) {
OSSched(); }
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100. ECB (Event Control Block)
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101. Event Control Block typedef struct {
void *OSEventPtr; /* Ptr to message or queue structure */
INT8U OSEventTbl[OS_EVENT_TBL_SIZE]; /* Wait list for event to occur */
INT16U OSEventCnt; /* Count (when event is a semaphore) */
INT8U OSEventType; /* Event type */
INT8U OSEventGrp; /* Group for wait list */
} OS_EVENT;
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102. List of Free ECBs
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103. Wait Queue Functions
void OSEventTaskRdy (OS_EVENT *pevent, void *msg, INT8U msk) {
y = OSUnMapTbl[pevent->OSEventGrp];
bity = OSMapTbl[y];
x = OSUnMapTbl[pevent->OSEventTbl[y]];
bitx = OSMapTbl[x];
prio = (INT8U)((y << 3) + x);
if ((pevent->OSEventTbl[y] &= ~bitx) == 0) {
pevent->OSEventGrp &= ~bity; }
ptcb = OSTCBPrioTbl[prio];
ptcb->OSTCBDly = 0;
ptcb->OSTCBEventPtr = (OS_EVENT *)0;
ptcb->OSTCBMsg = msg;
ptcb->OSTCBStat &= ~msk;
if (ptcb->OSTCBStat == OS_STAT_RDY) {
OSRdyGrp |= bity;
OSRdyTbl[y] |= bitx; } }
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104. Wait Queue Functions void OSEventTaskWait (OS_EVENT *pevent) {
OSTCBCur->OSTCBEventPtr = pevent;
if ((OSRdyTbl[OSTCBCur->OSTCBY] &= ~OSTCBCur->OSTCBBitX) == 0) {
OSRdyGrp &= ~OSTCBCur->OSTCBBitY; }
pevent->OSEventTbl[OSTCBCur->OSTCBY] |= OSTCBCur->OSTCBBitX;
pevent->OSEventGrp |= OSTCBCur->OSTCBBitY; }
void OSEventTO (OS_EVENT *pevent) {
if ((pevent->OSEventTbl[OSTCBCur->OSTCBY] &= ~OSTCBCur->OSTCBBitX) == 0) {
pevent->OSEventGrp &= ~OSTCBCur->OSTCBBitY; }
OSTCBCur->OSTCBStat = OS_STAT_RDY;
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
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105. Semaphore
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106. Creating a Semaphore OS_EVENT *OSSemCreate (INT16U cnt) {
pevent = OSEventFreeList;
if (OSEventFreeList != (OS_EVENT *)0) {
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr; }
if (pevent != (OS_EVENT *)0) {
pevent->OSEventType = OS_EVENT_TYPE_SEM;
pevent->OSEventCnt = cnt;
OSEventWaitListInit(pevent); }
return (pevent); }
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107. Waiting for a Semaphore
void OSSemPend (OS_EVENT *pevent, INT16U timeout, INT8U *err) {
if (pevent->OSEventCnt > 0) {
pevent->OSEventCnt--;
} else if (OSIntNesting > 0) {
*err = OS_ERR_PEND_ISR;
} else {
OSTCBCur->OSTCBStat |= OS_STAT_SEM;
OSTCBCur->OSTCBDly = timeout;
OSEventTaskWait(pevent);
OSSched();
if (OSTCBCur->OSTCBStat & OS_STAT_SEM) {
OSEventTO(pevent);
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0; } }
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108. Signaling a Semaphore INT8U OSSemPost (OS_EVENT *pevent) {
if (pevent->OSEventGrp) {
OSEventTaskRdy(pevent, (void *)0, OS_STAT_SEM);
OSSched();
return (OS_NO_ERR);
} else {
if (pevent->OSEventCnt < 65535) {
pevent->OSEventCnt++;
return (OS_SEM_OVF); } }
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109. Getting a Semaphore without Waiting
INT16U OSSemAccept (OS_EVENT *pevent) {
cnt = pevent->OSEventCnt;
if (cnt > 0) {
pevent->OSEventCnt--; }
return (cnt);
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110. Obtaining the Status of a Semaphore
INT8U OSSemQuery (OS_EVENT *pevent, OS_SEM_DATA *pdata) {
pdata->OSEventGrp = pevent->OSEventGrp;
psrc = &pevent->OSEventTbl[0];
pdest = &pdata->OSEventTbl[0];
for (i = 0; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++; }
pdata->OSCnt = pevent->OSEventCnt;
return (OS_NO_ERR); }
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111. Message Mailbox
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112. Creating a Mailbox OS_EVENT *OSMboxCreate (void *msg) {
pevent = OSEventFreeList;
if (OSEventFreeList != (OS_EVENT *)0) {
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr; }
if (pevent != (OS_EVENT *)0) {
pevent->OSEventType = OS_EVENT_TYPE_MBOX;
pevent->OSEventPtr = msg;
OSEventWaitListInit(pevent);
return (pevent);
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113. Waiting for a Message to Arrive at a Mailbox
void *OSMboxPend (OS_EVENT *pevent, INT16U timeout, INT8U *err) {
msg = pevent->OSEventPtr;
if (msg != (void *)0) {
pevent->OSEventPtr = (void *)0;
} else if (OSIntNesting > 0) {
*err = OS_ERR_PEND_ISR;
} else {
OSTCBCur->OSTCBStat |= OS_STAT_MBOX;
OSTCBCur->OSTCBDly = timeout;
OSEventTaskWait(pevent);
OSSched();
if ((msg = OSTCBCur->OSTCBMsg) != (void *)0) {
OSTCBCur->OSTCBMsg = (void *)0;
OSTCBCur->OSTCBStat = OS_STAT_RDY;
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
} else if (OSTCBCur->OSTCBStat & OS_STAT_MBOX) {
OSEventTO(pevent); }
return (msg);
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114. Depositing a Message in a Mailbox
INT8U OSMboxPost (OS_EVENT *pevent, void *msg) {
if (pevent->OSEventGrp) {
OSEventTaskRdy(pevent, msg, OS_STAT_MBOX);
OSSched();
return (OS_NO_ERR);
} else {
if (pevent->OSEventPtr != (void *)0) {
return (OS_MBOX_FULL);
pevent->OSEventPtr = msg;
return (OS_NO_ERR); } }
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115. Getting a Message without Waiting
void *OSMboxAccept (OS_EVENT *pevent) {
msg = pevent->OSEventPtr;
if (msg != (void *)0) {
pevent->OSEventPtr = (void *)0; }
return (msg); }
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116. Obtaining the Status of a Mailbox
INT8U OSMboxQuery (OS_EVENT *pevent, OS_MBOX_DATA *pdata) {
pdata->OSEventGrp = pevent->OSEventGrp;
psrc = &pevent->OSEventTbl[0];
pdest = &pdata->OSEventTbl[0];
for (i = 0; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++; }
pdata->OSMsg = pevent->OSEventPtr;
return (OS_NO_ERR); }
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117. Using a Mailbox as a Binary Semaphore
void Task1 (void *pdata) {
for (;;) {
OSMboxPend(MboxSem, 0, &err); /* Obtain access to resource(s) */ .
. /* Task has semaphore, access resource(s) */
OSMboxPost(MboxSem, (void )1); /* Release access to resource(s) */ }
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118. Using a Mailbox as a Time Delay
void Task1 (void *pdata) {
for (;;) {
OSMboxPend(MboxTimeDly, TIMEOUT, &err); /* Delay task */ .
. /* Code executed after time delay */ }
void Task2 (void *pdata) {
OSMboxPost(MboxTimeDly, (void *)1); /* Cancel delay for Task1 */
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119. Message Queues OSQCreate() OSQPend() OSQPost() OSQPostFront()
OSQAccept()
OSQFlush()
OSQQuery()
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120. Message Queues A message queue
Allows a task or an ISR to send pointer size variables to another task.
Each pointer points a specific data structure containing a ‘message’.
Looks like a mailbox with multiple entries.
Is like an array of mailboxes except that there is only one wait list.
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121. Message Queues (Cont.)
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122. Data Structures in a Message Queue
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123. Queue Control Block A queue control block contains following fields
OSQPtr
OSQStart
OSQEnd
OSQIn
OSQOut
OSQSize
OSQEntries
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124. List of Free Queue Control Blocks
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125. Message Queue Is a Circular Buffer
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126. Creating a Queue Specify the number of entries.
OSQCreate() requires that you allocate an array of pointers that hold the message.
The array must be declared as an array of pointers to void.
Once a message queue has been created, it cannot be deleted.
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127. OSQCreate() OS_EVENT *OSQCreate (void **start, INT16U size) {
pevent = OSEventFreeList;
if (OSEventFreeList != (OS_EVENT *)0) {
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr; }
if (pevent != (OS_EVENT *)0) {
pq = OSQFreeList;
if (OSQFreeList != (OS_Q *)0) {
OSQFreeList = OSQFreeList->OSQPtr;
if (pq != (OS_Q *)0) {
pevent->OSEventType = OS_EVENT_TYPE_Q;
pevent->OSEventPtr = pq;
OSEventWaitListInit(pevent);
} else {
pevent->OSEventPtr = (void *)OSEventFreeList;
OSEventFreeList = pevent;
pevent = (OS_EVENT *)0;
return (pevent);
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128. OSQPend() (1)
void *OSQPend (OS_EVENT *pevent, INT16U timeout, INT8U *err) {
pq = pevent->OSEventPtr;
if (pq->OSQEntries != 0) {
msg = *pq->OSQOut++;
pq->OSQEntries--;
if (pq->OSQOut == pq->OSQEnd) {
pq->OSQOut = pq->OSQStart; }
*err = OS_NO_ERR;
} else if (OSIntNesting > 0) {
*err = OS_ERR_PEND_ISR;
} else {
OSTCBCur->OSTCBStat |= OS_STAT_Q;
OSTCBCur->OSTCBDly = timeout;
OSEventTaskWait(pevent);
OSSched();
if ((msg = OSTCBCur->OSTCBMsg) != (void *)0) {
OSTCBCur->OSTCBMsg = (void *)0;
OSTCBCur->OSTCBStat = OS_STAT_RDY;
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
*err = OS_NO_ERR;
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129. OSQPend() (2) } else if (OSTCBCur->OSTCBStat & OS_STAT_Q) {
OSEventTO(pevent);
msg = (void *)0;
*err = OS_TIMEOUT;
} else {
msg = *pq->OSQOut++;
pq->OSQEntries--;
if (pq->OSQOut == pq->OSQEnd) {
pq->OSQOut = pq->OSQStart; }
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
*err = OS_NO_ERR;
return (msg);
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130. OSQPost() INT8U OSQPost (OS_EVENT *pevent, void *msg) {
if (pevent->OSEventGrp) {
OSEventTaskRdy(pevent, msg, OS_STAT_Q);
OSSched();
return (OS_NO_ERR);
} else {
pq = pevent->OSEventPtr;
if (pq->OSQEntries >= pq->OSQSize)
return (OS_Q_FULL);
else {
*pq->OSQIn++ = msg;
pq->OSQEntries++;
if (pq->OSQIn == pq->OSQEnd) {
pq->OSQIn = pq->OSQStart; }
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131. OSQPostFront() OSQPostFront() Is basically identical to OSQPost().
Uses OSQOut instead of OSQIn as the pointer to the next entry.
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132. OSQPostFront() (Cont.)
INT8U OSQPostFront (OS_EVENT *pevent, void *msg){
if (pevent->OSEventGrp) {
OSEventTaskRdy(pevent, msg, OS_STAT_Q);
OSSched();
return (OS_NO_ERR);
} else {
pq = pevent->OSEventPtr;
if (pq->OSQEntries >= pq->OSQSize)
return (OS_Q_FULL);
else {
if (pq->OSQOut == pq->OSQStart) {
pq->OSQOut = pq->OSQEnd; }
pq->OSQOut--;
*pq->OSQOut = msg;
pq->OSQEntries++;
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133. OSQAccept() void *OSQAccept (OS_EVENT *pevent) {
pq = pevent->OSEventPtr;
if (pq->OSQEntries != 0) {
msg = *pq->OSQOut++;
pq->OSQEntries--;
if (pq->OSQOut == pq->OSQEnd) {
pq->OSQOut = pq->OSQStart; }
} else {
msg = (void *)0;
return (msg);
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134. OSQFlush() INT8U OSQFlush (OS_EVENT *pevent) {
pq = pevent->OSEventPtr;
pq->OSQIn = pq->OSQStart;
pq->OSQOut = pq->OSQStart;
pq->OSQEntries = 0;
return (OS_NO_ERR); }
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135. OSQQuery() Pass a OS_Q_DATA structure to query.
OS_Q_DATA contains following fields
OSMsg
OSNMsgs
OSQSize
OSEventTbl[]
OSEventGrp
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136. OSQQuery() (Cont.)
INT8U OSQQuery (OS_EVENT *pevent, OS_Q_DATA *pdata){
pdata->OSEventGrp = pevent->OSEventGrp;
psrc = &pevent->OSEventTbl[0];
pdest = &pdata->OSEventTbl[0];
for (i = 0; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++; }
pq = (OS_Q *)pevent->OSEventPtr;
if (pq->OSQEntries > 0) {
pdata->OSMsg = pq->OSQOut;
} else {
pdata->OSMsg = (void *)0;
pdata->OSNMsgs = pq->OSQEntries;
pdata->OSQSize = pq->OSQSize;
return (OS_NO_ERR);
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137. Using a Message Queue When Reading Analog Inputs
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138. Using a Queue as a Counting Semaphore
void main (void){
OSInit(); …
QSem = OSQCreate(&QMsgTbl[0], N_RESOURCES);
for (i = 0; i < N_RESOURCES; i++) {
OSQPost(Qsem, (void *)1); }
OSTaskCreate(Task1, .., .., ..);
OSStart();
void Task1 (void *pdata) {
for (;;) {
OSQPend(&QSem, 0, &err); /* Obtain access to resource(s) */
Task has semaphore, access resource(s)
OSMQPost(QSem, (void )1); /* Release access to resource(s) */
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139. uC/OS-II Real-Time Systems Concepts Kernel Structure Task Management
Time Management
Intertask Communication & Synchronization
Memory Management
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140. Memory Management Overview Memory Control Blocks OSMemCreate()
OSMemGet()
OSMemPut()
OSMemQuery()
Examples
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141. ANSI C malloc() and free()
Dangerous in an embedded real-time system.
Fragmentation.
Non-deterministic.
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142. µC/OS-II malloc() and free()
Obtain a contiguous memory area.
Memory blocks are the same size.
Partition contains an integral number of blocks.
Allocation and de-allocation is deterministic.
More than one memory partition can exist.
Application can obtain memory blocks of different sizes.
Memory block must always be returned to the partition from which it came from.
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143. Multiple Memory Partitions
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144. Memory Control Blocks Keeps track of memory partitions through MCB.
Each memory partition requires its own memory control block.
Initialization is done by OSMemInit().
Number of memory partitions must be set to at least 2.
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145. Memory Control Block Data Structure
typedef struct {
void *OSMemAddr;
void *OSMemFreeList;
INT32U OSMemBlkSize;
INT32U OSMemNBlks;
INT32U OSMemNFree;
} OS_MEM;
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146. List of Free Memory Control Blocks
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147. OSMemCreate() (1)
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148. OSMemCreate() (2)
OS_MEM *OSMemCreate (void *addr, INT32U nblks, INT32U blksize, INT8U *err) {
pmem = OSMemFreeList;
if (OSMemFreeList != (OS_MEM *)0) {
OSMemFreeList = (OS_MEM *)OSMemFreeList>OSMemFreeList; }
if (pmem == (OS_MEM *)0) {
*err = OS_MEM_INVALID_PART;
return ((OS_MEM *)0);
plink = (void **)addr;
pblk = (INT8U *)addr + blksize;
for (i = 0; i < (nblks - 1); i++) {
*plink = (void *)pblk;
plink = (void **)pblk;
pblk = pblk + blksize;
*plink = (void *)0;
pmem->OSMemAddr = addr;
pmem->OSMemFreeList = addr;
pmem->OSMemNFree = nblks;
pmem->OSMemNBlks = nblks;
pmem->OSMemBlkSize = blksize;
*err = OS_NO_ERR;
return (pmem);
>2 entry, entry size>a pointer
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149. OSMemGet() void *OSMemGet (OS_MEM *pmem, INT8U *err) {
if (pmem->OSMemNFree > 0) {
pblk = pmem->OSMemFreeList;
pmem->OSMemFreeList = *(void **)pblk;
pmem->OSMemNFree--;
*err = OS_NO_ERR;
return (pblk);
} else {
*err = OS_MEM_NO_FREE_BLKS;
return ((void *)0); }
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150. Returning a Memory Block
INT8U OSMemPut (OS_MEM *pmem, void *pblk) {
if (pmem->OSMemNFree >= pmem->OSMemNBlks)
return (OS_MEM_FULL);
*(void **)pblk = pmem->OSMemFreeList;
pmem->OSMemFreeList = pblk;
pmem->OSMemNFree++;
return (OS_NO_ERR); }
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151. Obtaining Status about Memory Partition
Pass a OS_MEM_DATA structure to query.
OS_MEM_DATA contains following fields
OSAddr
OSFreeList
OSBlkSize
OSNBlks
OSNFree
OSNUsed
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152. OSMemQuery() INT8U OSMemQuery (OS_MEM *pmem, OS_MEM_DATA *pdata) {
pdata->OSAddr = pmem->OSMemAddr; (1)
pdata->OSFreeList = pmem->OSMemFreeList;
pdata->OSBlkSize = pmem->OSMemBlkSize;
pdata->OSNBlks = pmem->OSMemNBlks;
pdata->OSNFree = pmem->OSMemNFree;
pdata->OSNUsed = pdata->OSNBlks - pdata->OSNFree; (2)
return (OS_NO_ERR); }
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153. Using Dynamic Memory Allocation
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154. Waiting for Memory Blocks (1)
Sometimes it’s useful to have a task wait for a memory block in case a partition runs out of blocks.
µC/OS-II doesn’t support ‘pending’ on a partitions.
Can support this requirement by adding a counting semaphore.
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155. Waiting for Memory Blocks (2)
void main (void) { …
SemaphorePtr = OSSemCreate(100);
PartitionPtr = OSMemCreate(Partition, 100, 32, &err);
OSTaskCreate(Task, (void *)0, &TaskStk[999], &err);
OSStart(); }
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156. Waiting for Memory Blocks (3)
void Task (void *pdata) {
INT8U err;
INT8U *pblock;
for (;;) {
OSSemPend(SemaphorePtr, 0, &err);
pblock = OSMemGet(PartitionPtr, &err);
/* Use the memory block */
OSMemPut(PartitionPtr, pblock);
OSSemPost(SemaphorePtr); }
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