Embedded System Presentation Nguyễn Trần Quang Nguyễn Công Vũ 1µC/OS-II.

1

Embedded System Presentation

Nguyễn Trần QuangNguyễn Công Vũ

µC/OS-II

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µC/OS-II

µC/OS-II

Micro C_OS 3

Outline

• Introduction to µC/OS-II• Kernel Structure• Task Management• Time Management• Semaphore Management• Mutual Exclusion Semaphores• Event Flag Management• Message Mailbox Management• Message Queue Management• Memory Management

Micro C_OS 4

Outline


Micro C_OS 5

At the Beginning

• Written By J. Labrosse• First published in 1992

• µC/OS-II is a trade mark of Micrium.• 1000s applications are using it all over the world.• A good starting point to experience real-time OS• Simple but yet very powerful

Micro C_OS 6

µC/OS-II in Literature

• Four books were published to explain the internals:• “μC/OS The Real-Time Kernel”, in 1992• “μC/OS-II The Real-Time Kernel”, in 1998• “μC/OS-II The Real-Time Kernel”, Second Edition in

2002• “μC/OS-III The Real-Time Kernel”, in 2009

Micro C_OS 7

µC/OS-II History

µC/OS-IIV2.86

µC/OS-IIV2.52

µC/OS-IIV2.00

µC/OSV1.08

µC/OS-III

µC/OS V1.08+

Memory Manager +

Stack Checking +

CPU Load Checking

µC/OS-II V2.00+

Safety Critical+

Mutexes+

Semaphores+

Event Flags

µC/OS-II V2.52+

Timers+

250 Tasks+

MMU & MPU

µC/OS-II V2.86+

RR Scheduling+

Infinite # of Tasks&

Services

Micro C_OS 8

µC/OS-II Features

• Source code• Portable• Preemptive• Multitasking• Task stack• Services• Interrupt management• Robust & reliable• …

Micro C_OS 9

Source Code

• High quality• Neat• Consistent• Organized• Commented• MISRA-C compliant

Micro C_OS 10

Source Code

• Highly portable ANSI C• Assembly is kept minimum• Supports 8-, 16-, 32-, 64- bit processors• Ported over 100 different processors• All ports are freely available at Micrium website

Micro C_OS 11Amr Ali Abdel-Naby@2010 Introduction to uCOS-II V2.6

Micro C_OS 12

Preemptive

• Fully preemptive• Always runs the highest priority task that is

ready to run

Micro C_OS 13

Multitasking

• Manages up to 64 tasks• 8 tasks are used by µC/OS-II• 56 tasks are left to applications• A unique task/priority• RR and FIFO are not supported

Micro C_OS 14

Task Stacks

• Each task has its stack• μC/OS-II allows different stack sizes• Stack checking utility• You can determine & decide how much stack is

needed for each task

Micro C_OS 15

Task Stacks

• Each task has its stack• μC/OS-II allows different stack sizes• Stack checking utility• You can determine & decide how much stack is

needed for each task

Micro C_OS 16

Services

• Semaphores• Mutexes• Event flags• Message queues• Mailboxes• Fixed size memory partitions• Task management• Time management

Micro C_OS 17

Interrupt Management

• An interrupt can suspend a task execution• The highest priority ready task runs after serving

the interrupt• Nested interrupts

• Up to 255 level

Micro C_OS 18

Robust & Reliable

• Used by many products• Support• Tested & certified in safety critical systems

Micro C_OS 19

Related Products

• µC/Probe• µC/TCP-IP• µC/FS• µC/GUI• µC/USB• µC/CAN• µC/Modbus• µC/FL• µC/Building Blocks• µC/OSEK-VDX

Micro C_OS 20

µC/OS-II Market

• Distributors all over the word• Huge customer list

Micro C_OS 21

License

• Educational• Free• Universities• Non-profitable use

• Source Code• If µC/OS will be distributed with your product as a

source code

• Object Code• If µC/OS will be distributed with your product as a

binary

• Not royalty free

Micro C_OS 22

Outline


Micro C_OS 23

Outline


Micro C_OS 24

Kernel Architecture

µC/OS-II Port(Processor Specific Code)

µC/OS-II(Processor Independent

code)

µC/OS-II Configuration(Application Specific)

Application SW(Your Code)

HW

Micro C_OS 25

Critical Sections

• 2 macros protect critical sections• They enable/disable interrupts

• Can be used by your application• Not a good programming style• Applications may crash

• Processor & tool chain specific

OS_ENTER_CRITICAL();/* Critical Code */OS_EXIT_CRITICAL();

Micro C_OS 26

Tasks

• Distributors all over the word• Huge customer list

• Lowest priority is defined

as OS_LOWEST_PRIO

/* Endless Loop Task */void My_Task (void * pdata){for(;;){/* Your Code */}}

/* Run To Completion Task */void My_Task (void * pdata){/* Your Code */OSTaskDel(OS_PRIO_SELF);}

Up to 56 application tasks

0

1

2

3

…

60

61

62

63

Pri

ori

ty

Used by the system

May be used in the future

extension of μC/OS-II

Micro C_OS 27

Task States

Micro C_OS 28

Task Control Blocks

• µC/OS-II uses TCBs for task management• Every task is assigned a TCB when created

Micro C_OS 29

Task Control Blocks cont’d

• A TCB contains:• Task’s priority• Task’s state• A pointer to the task’s top of stack• Other task’s related data

• TCBs reside in RAM

Micro C_OS 30

Ready List

• The kernel maintains a list of tasks that can be ready to run

• The highest priority task is kept at the beginning of the task

Micro C_OS 31

Task Scheduling

• Task-level scheduling is performed by OS_Sched

• ISR-level scheduling is handled by OSIntExit• Task Level context switch

Micro C_OS 32

Locking & Unlocking the Scheduler• A mechanism used by a task to keep control of

the CPU, even if there are higher priority tasks ready

• Two kernel services are provided & must be used in pairs:• OSSchedLock & OSSchedUnlock

• After calling OSSchedLock, your application should not call a service that suspends execution• Your application will crashLPT

HPT

LPT

OSSchedLock OSSchedUnlockHPT is ready here

Micro C_OS 33

Idle Task

• Executed when there is no other task ready to run• Always set to the lowest priority

Micro C_OS 34

Statistics Task

• Its priority is higher than IDLE task by 1• It provides runtime statistics• It is called OS_TaskStat & it is called every

second• It tells you how long was the CPU used by your

application• To use it, you must call OSStatInit from the first

& the only task created during initialization

Micro C_OS 35

Statistics Task

void main(void){OSInit();...Create your startup task TaskStart()...OSStart();}void TaskStart(void * pdata){OSStatInit();...}

Micro C_OS 36

Interrupts Under µC/OS-II

• You should keep ISRs as short as possible• Interrupts either use an interrupt stack or task

stack• Stack size must account for:

• ISR nesting• Function call nesting• Local variables

Micro C_OS 37

Clock Tick

• µC/OS-II requires a periodic time source to keep track of time delays & timeouts

• Ticker interrupts must be enabled after starting multitasking

• The clock tick is serviced by calling OSTimeTick from the tick ISR

void main(void){OSInit();...Enable Ticker Interrupt /* Mistake */...OSStart();}

Micro C_OS 38

µC/OS-II Initialization

• µC/OS-II requires that OSInit is called before any other service

• It initializes all µC/OS-II variables & data structures

• It creates idle & statistics tasks

void main(void){OSInit();...OSStart();}

Micro C_OS 39

Starting µC/OS-II

• Multitasking is started by calling OSStart after creating at least 1 task

void main(void){OSInit();...Create at least 1 task here...OSStart();}

Micro C_OS 40

Obtaining the Current Version

• By calling OSVersion

Micro C_OS 41

Outline


Micro C_OS 42

Outline


Micro C_OS 43

Micro C_OS 44

Creating a Task, OSTaskCreate

• INT8U OSTaskCreate (void (*task)(void *pd), void *pdata, OS_STK *ptos, INT8U prio)• task: A pointer to the task's code• pdata: A pointer to an optional data area which can be used to

pass parameters to the task when the task first executes• ptos: A pointer to the task's top of stack• prio: The task's priority• Return value:o No erroro Priority existo Invalid priority

Micro C_OS 45

Creating a Task, 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)• OSTaskCreate +• id: Task’s ID, not used currently• pbos: A pointer to the task's bottom of stack• stk_size: A pointer to the task's top of stack• pext: A pointer to a user supplied memory location which is used

as a TCB extension• opt: Additional information (or options) about the behavior of the

task

Micro C_OS 46

Task Stacks

• Each task has its own stack.• It must be:

• Declared as OS_STK• Consistent & contiguous memory

• It can be allocated static

• Or dynamic

OS_STK MyTaskSTack[stack_size];

OS_STK *pstk;...pstk = (OS_STK*)malloc(stack_size);

Micro C_OS 47

Naming a Task, OSTaskNameSet

• void OSTaskNameSet (INT8U prio, char *pname, INT8U *err)• prio: The priority of the task that you want to assign a name to• pname: A pointer to an ASCII string that contains the name of the task • err:o No erroro Task does not exist.o Name too longo A null pointer is passed for the name.o Invalid priority

Micro C_OS 48

Outline


Micro C_OS 49

Outline


Micro C_OS 50

Time Management APIs

• Available time operations are:• Delaying a task• Resuming a delayed task• System time getting & setting

Micro C_OS 51

Delaying a Task, OSTimeDly

• void OSTimeDly (INT16U ticks)• ticks: The time delay that the task will be suspended in number of

clock ticks

time10ms

OSTickISR()

All HPT

LPT

5ms

OSTimeDly(1)

Micro C_OS 52

Delaying a Task, OSTimeDlyHMSM

• INT8U OSTimeDlyHMSM (INT8U hours, INT8U minutes, INT8U seconds, INT16U milli)• hours: The number of hours that the task will be delayed • minutes: The number of minutes• seconds: The number of seconds• milli: The number of milliseconds• Return value:o No erroro Zero delayo Invalid minutes, seconds, & milli seconds

Micro C_OS 53

Resuming a Delayed Task, OSTimeDlyResume

• INT8U OSTimeDlyResume (INT8U prio)• prio: Specifies the priority of the task to resume• Return value:o No erroro Invalid priorityo Task is not delayed.o Task does not exist.

Micro C_OS 54

System Time, OSTimeSet

• void OSTimeSet (INT32U ticks)• ticks: Specifies the new value that OSTime needs to take

Micro C_OS 55

System Time, OSTimeGet

• INT32U OSTimeGet (void)• Return value:o The current value of OSTime

Micro C_OS 56

Outline


Micro C_OS 57

Outline


Micro C_OS 58

Semaphores

• Semaphores are 16 bit unsigned integers used for resource sharing or to signal the occurrence of an event

OSSemCreate()OSSemDel()OSSemPost()

OSSemAccept()OSSemPend()OSSemQuery()

OSSemPost()

N

NOSSemAccept()

ISR

ISR

Task

Task

Micro C_OS 59

Semaphores

Functions:• Creating a Semaphore, OSSemCreate• Deleting a Semaphore, OSSemDel• Waiting on a Semaphore (Blocking), OSSemPend• Signaling a Semaphore, OSSemPost• Getting a Semaphore without Waiting, OSSemAccept• Obtaining the Status of a Semaphore, OSSemQuery• Creating a Semaphore, OSSemCreate• Obtaining the Status of a Semaphore, OSSemQuery

Micro C_OS 60

Outline


Micro C_OS 61

Mutexes

• They are used to gain exclusive access to resources.• They reduce priority inversion problem (priority ceiling protocol

is supported).

OSMutexCreate()OSMutexDel()OSMutexPost()

OSMutexPend()OSMutexAccept()OSMutexQuery()

Task Task

Micro C_OS 62

Creating a Mutex, OSMutexCreate

OS_EVENT *OSMutexCreate (INT8U prio, INT8U *err)• prio: Ceiling priroity• err:

o No erroro Called from ISRo Priority existso Invalid priorityo No available resources

• Return value:o Non-null for successful creationo Null for failure

Micro C_OS 63

Deleting a Mutex, OSMutexDel

OS_EVENT *OSMutexDel (OS_EVENT *pevent, INT8U opt, INT8U *err)• pevent: A pointer to the mutex to be deleted• opt: Delete options

o Delete alwayso Delete if no pending tasks

• err:o No erroro Called from ISRo Invalid optiono There are tasks pending.o pevent is null.o pevent is not a semaphore.

Micro C_OS 64

Deleting a Mutex, OSMutexDel cont’d

OS_EVENT *OSMutexDel (OS_EVENT *pevent, INT8U opt, INT8U *err)• Return value: Null if successful

Micro C_OS 65

Waiting on a Mutex (Blocking), OSMutexPend

void OSMutexPend (OS_EVENT *pevent, INT16U timeout, INT8U *err)• pevent: A pointer to the mutex to acquire• timeout:

o 0 wait for evero !0 wait with specific timeout

• err:o No erroro Timeouto pevent is not a mutex.o pevent is null.o Called from ISR

Micro C_OS 66

Signaling a Mutex, OSMutexPost

INT8U OSMutexPost (OS_EVENT *pevent)• pevent: A pointer to the mutex to release• Return value:

o No erroro Not mutex ownero Called from ISRo pevent is not a mutex.o pevent is null.

Micro C_OS 67

Getting a Mutex without Waiting, OSMutexAccept

INT8U OSMutexAccept (OS_EVENT *pevent, INT8U *err)• pevent: A pointer to the mutex to acquire • err:

o No erroro Called from ISRo pevent is not a mutex.o pevent is null.

• Return value:o 1 resource availableo 0 case of error or mutex is no available

Micro C_OS 68

Obtaining the Status of a Mutex, OSMutexQuery

INT8U OSMutexQuery (OS_EVENT *pevent, OS_MUTEX_DATA *pdata)• pevent: A pointer to the desired mutex• pdata: A pointer to the returned mutex information• Return value:

o No erroro Called from ISRo pevent is not a mutex.o pevent is null.

Micro C_OS 69

Outline


Micro C_OS 70

Event Flags

• Used for synchronization of tasks with the occurrence of multiples of events

• Events are groupedo 8, 16 or 32 bits per group

• Types of synchronizationo ORed: Any event occurredo ANDed: All events occured

Micro C_OS 71Amr Ali Abdel-Naby@2010 Introduction to uCOS-II V2.6

Event Flags cont’d

Micro C_OS 72

Event Flags Management APIs

OSFlagPost()

OSFlagCreate ()OSFlagDel()OSFlagPost () OSFlagAccept ()

OSFlagPend ()OSQFlagQuery ()

ISR

Task

ISR

Task

OSFlagAccept ()OSQFlagQuery ()

Micro C_OS 73

Outline


Micro C_OS 74

Message Mailboxes

• A message mailbox is a μC/OS-II object that allows a task or an ISR to send pointer-sized variable to another task.

OSMboxCreate()

MessageOSMboxPost()OSMboxAccept()

OSMboxPost()

OSMboxPend()OSMboxAccept()OSMboxQuery()

ISR

Task

Task

Micro C_OS 75

Outline


Micro C_OS 76

Message Queues

• A message queue is a μC/OS-II object that allows a task or an ISR to send pointer-sized variables to another task.

OSQCreate()

Message

OSQPost()OSQPostFront()OSQFlush()OSQAccept()OSQPostOpt()

OSQPost()OSQPostFront()OSQFlush()OSQPostOpt()

OSQPend()OSQAccept()OSQQuery()

ISR

Task

Task

Micro C_OS 77

Outline


Micro C_OS 78

Memory Management

• Fixed-size memory block managemento To prevent fragmentation

• Multiple partitions can be created with different sizes.

• Blocks allocated from certain partitions must be returned back to the same partitions

Micro C_OS 79

Memory Management

Micro C_OS 80

Memory Management

Micro C_OS 81

Memory Management APIs

• Available memory operations are:o Creating a memory partitiono Obtaining a memory blocko Returning a memory blocko Obtaining status of a memory partitiono Naming a memory partitiono Getting the name of a memory partition

Embedded System Presentation Nguyễn Trần Quang Nguyễn Công Vũ 1µC/OS-II.

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