freeRTOS_taskmanagement

7/29/2019 freeRTOS_taskmanagement

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ARM PROGRAMMING

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Why use RTOS

Three sources of LCD messagesMix of fast and slow hardwareMix of continuous, periodic, event driven, highpriority and low priority requirements


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Why use RTOS

Concurrent processing


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Scheduler

Scheduler l 1 phn ca kernel dng quytnh tc v no c chy ti mi thi im.

Kernel c th dng v phc hi hot ng ca1 tc v trong khi tc v ang chy.

Mt tc v c th dng chnh n bng cchdelay (sleep) mt khong thi gian, hoc ch(block) i mt s kin (vd: keypressed)hay 1 ti nguyn (vd: serialport)

Scheduler


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Scheduler

At (1) task 1 is executing. At (2) the kernel suspends task 1 ... and at (3) resumes task 2. While task 2 is executing (4), it locks a

processor peripheral for it's ownexclusive access.

At (5) the kernel suspends task 2 ... ... and at (6) resumes task 3.

Scheduler Task 3 tries to access the same processor

peripheral, finding it locked, task 3 cannotcontinue so suspends itself at (7).

At (8) the kernel resumes task 1. Etc. The next time task 2 is executing (9) it finishes

with the processor peripheral and unlocks it. The next time task 3 is executing (10) it finds it

can now access the processor peripheral and this time executes

until suspended by the kernel.


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Realtime scheduler

Mi tc v phi p ng (response)trong thi gian qui nh (deadline).

Mi tc v c 1 mc u tin ring

Scheduler s m bo tc v c quynu tin cao lun c thc thi bngcch tm dng tc v c quyn u tinthp.

Realtime OS

DisplayKeypad LCD

ADCAnalog Input

filter

Sample rate: 5Khz

Response time: 0-100ms

controloutput


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Keypad handler

void vKeyHandlerTask( void *pvParameters ){

// Key handling is a continuous process and as such the task// is implemented using an infinite loop (as most real time// tasks are).for( ;; ){

[Suspend waiting for a key press][Process the key press]

}}

controlvoid vControlTask( void *pvParameters ){

for( ;; ){

[Suspend waiting for 0.5ms since the start of the previouscycle][Sample the input][Filter the sampled input][Perform control algorithm][Output result]

}}


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Mc u tin

Deadline ca tc v control th nghimngt hn ca tc v keypad.

Hu qu ca vic tr deadline ca tc vcontrol th ln hn so vi keypad


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FreeRTOS realtime kernel

Example using FreeRTOSint main( void ){/* Create the 2 task in exactly the same way. */

xTaskCreate( vTask1, "Task 1", 1000, NULL, 1, NULL );xTaskCreate( vTask2, "Task 2", 1000, NULL, 1, NULL );

/* Start the scheduler so our tasks start executing.*/

vTaskStartScheduler();/* If all is well we will never reach here as the

scheduler will now be running. If we do reachhere then it is likely that there was insufficient

heap available for the idle task to be created. */for( ;; );return 0;

}


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Example using FreeRTOS

void vTask1( void *pvParameters ){const char *pcTaskName = "Task 1 is running\r\n";volatile unsigned long ul;

/* As per most tasks, this task is implemented in an infiniteloop. */

for( ;; ){

/* Print out the name of this task. */vPrintString( pcTaskName );/* Delay for a period. */for( ul = 0; ul < mainDELAY_LOOP_COUNT; ul++ )

{ }}

}

Example using FreeRTOSvoid vTask2( void *pvParameters ){const char *pcTaskName = "Task 2 is running\r\n";volatile unsigned long ul;

/* As per most tasks, this task is implemented in an infiniteloop. */

for( ;; ){

/* Print out the name of this task. */vPrintString( pcTaskName );

/* Delay for a period. */for( ul = 0; ul < mainDELAY_LOOP_COUNT; ul++ ){

}}

}


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The actual execution pattern of thetwo tasks

FreeRTOS source code structure


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freeRTOSconfig.h

#define configUSE_PREEMPTION 1#define configUSE_IDLE_HOOK 0#define configUSE_TICK_HOOK 1#define configCPU_CLOCK_HZ ( ( unsigned long ) 50000000 )#define configTICK_RATE_HZ ( ( portTickType ) 1000 )#define configMINIMAL_STACK_SIZE ( ( unsigned short ) 70 )#define configTOTAL_HEAP_SIZE ( ( size_t ) ( 24000 ) )#define configMAX_TASK_NAME_LEN ( 12 )#define configUSE_TRACE_FACILITY 1#define configUSE_16_BIT_TICKS 0#define configIDLE_SHOULD_YIELD 0#define configUSE_CO_ROUTINES 0#define configUSE_MUTEXES 1

#define configUSE_RECURSIVE_MUTEXES 1#define configCHECK_FOR_STACK_OVERFLOW 2

freeRTOSconfig.h#define configMAX_PRIORITIES ( ( unsigned portBASE_TYPE ) 5 )#define configMAX_CO_ROUTINE_PRIORITIES ( 2 )#define configQUEUE_REGISTRY_SIZE 10

/* Set the following definitions to 1 to include the API function, or zeroto exclude the API function. */

#define INCLUDE_vTaskPrioritySet 1#define INCLUDE_uxTaskPriorityGet 1#define INCLUDE_vTaskDelete 1

#define INCLUDE_vTaskCleanUpResources 0#define INCLUDE_vTaskSuspend 1#define INCLUDE_vTaskDelayUntil 1#define INCLUDE_vTaskDelay 1#define INCLUDE_uxTaskGetStackHighWaterMark 1


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Task management

Tc v l 1 hm vi mt vng lp v tn.

void ATaskFunction( void *pvParameters ){int iVariableExample = 0;

/* A task will normally be implemented as in infinite loop. */for( ;; ){

[suspend waiting for a key press][process the key]

}

vTaskDelete( NULL );}

Task stateTc v chuyn t trng thi dng sang chy gi l swapped in,switched inTc v chuyn t trng thi chy sang dng gi l swapped out,switched out


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Task management function

CreationxTaskCreatexTaskDelete

ControlvTaskDelayvTaskDelayUntiluxTaskPriorityGetvTaskPrioritySetvTaskSuspendvTaskResume

xTaskResumeFromIS

UtilitiestskIDLE_PRIORITYxTaskGetTickCountuxTaskGetNumberOfTasksvTaskListvTaskGetRunTimeStatsvTaskStartTraceulTaskEndTraceuxTaskGetStackHighWaterMarkvTaskSetApplicationTaskTagxTaskSetApplicationTaskTagxTaskCallApplicationTaskHook

Naming convention


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Naming convention

Variables of type char are prefixed c Variables of type short are prefixed s Variables of type long are prefixed l Variables of type float are prefixed f Variables of type double are prefixed d Enumerated variables are prefixed e Other types (e.g. structs) are prefixed x Pointers have an additional prefixed p , for example a

pointer to a short will have prefix ps

Unsigned variables have an additional prefixed u , forexample an unsigned short will have prefix us

Naming convention File private functions are prefixed with prv API functions are prefixed with their return

type, as per the convention defined forvariables

Function names start with the file in which theyare defined. For example vTaskDelete isdefined in Task. c

x is used both for structures and for RTOStypes such as portTickType (in the ARM portthis is equivalent to unsigned int)


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Creating a Task, xTaskCreate

portBASE_TYPE xTaskCreate(

pdTASK_CODE pvTaskCode,

const signed portCHAR * const pcName,

unsigned portSHORT usStackDepth,

void *pvParameters,

unsignedportBASE_TYPE uxPriority,

xTaskHandle *pxCreatedTask

);

Creating a Task, xTaskCreate pvTaskCode: con tr ch n tn tc v

pcName: tn m t tc v (chiu di lnnht mc nh l 16)

usStackDepth: rng stack ca tc v.

pvParameters: con tr ch n tham s

a vo tc v.


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uxPriority: mc u tin ca tc v. C gi tr t 0 n

(configMAX_PRIORITIES 1)

0 l mc u tin thp nht

pxCreatedTask: dng tr v handleca tc v

Creating a Task, xTaskCreate Gi tr tr v:

pdPass nu thnh cng

errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY n tc v khng th c khito


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xTaskCreate( vTask1,/* Pointer to the function that implements the task. */

"Task 1",/* Text name for the task. This is to facilitate debugging

only. */1000,

/* Stack depth - most small microcontrollers will use muchless stack than this. */

NULL, /* We are not using the task parameter. */1, /* This task will run at priority 1. */NULL ); /* We are not going to use the task handle. */

Using the task paramettervoid vTaskFunction( void *pvParameters ){char *pcTaskName;volatile unsigned long ul;pcTaskName = ( char * ) pvParameters;

for( ;; ){

vPrintString( pcTaskName );

/* Delay for a period. */for( ul = 0; ul < mainDELAY_LOOP_COUNT; ul++ ) ;

}}


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Using the task parametter

static const char *pcTextForTask1 = Task 1 is running\r\n;static const char *pcTextForTask2 = Task 2 is running\t\n;int main( void ){

/* Create one of the two tasks. */xTaskCreate( vTaskFunction, "Task 1", 1000,

(void*)pcTextForTask1,/* Pass the text to be printed into the task

using the task parameter. */1, NULL );

xTaskCreate( vTaskFunction, "Task 2", 1000,(void*)pcTextForTask2, 1, NULL );

vTaskStartScheduler();for( ;; );}

Task priorities Tham s configMAX_PRIORITIES qui

nh s mc u tin c th c.

Nhiu tc v c th c cng mc u tin

Scheduler chy sau mi khong thigian xc nh (system tick).

Tham s configTICK_RATE_HZ qui nhkhong thi gian gia 2 ln systemTick.


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Task priorities

Cc API ca FreeRTOS lun dng sln systemTick xy ra m thi gian

Tham s portTICK_RATE_MS dng chuyn i t s ln sysTick sang thigian ms.

Task priorities


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2

Two task with different priorities





xTaskCreate( vTaskFunction, "Task 2", 1000,(void*)pcTextForTask2, 2, NULL );

vTaskStartScheduler();

for( ;; );}

Continous processing Trong cc v d trn, cc tc v lun

chy m khng cn i bt k s kinno.

V vy, cc tc v lun trng thi snsng chuyn sang Running

Chuyn g xy ra khi tc v dngny c u tin cao?


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2

Event driven task

Trong h thng nhng, cc tc vthng c thit k theo dng event-driven

Chng phi ch 1 s kin xy ra cth i vo trng thi Running

Scheduler s chn tc v c u tincao nht m c th chuyn sang trngthi Running.

Task state


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The Blocked State

Tc v i vo trng thi Block ch 2 dngevent sau:

Thi gian: mt khong thi gian delay hoc mt thi im xc

nh k t khi scheduler bt u chy.

Synchronization event: (s kin ng b) Khi s kin c to t 1 tc v khc hay interrupt.

FreeRTOS queues, binary semaphores,

counting semaphores, recursive semaphores,mutexes c th dng to synchronization event.

The Suspended State Tc v b trong trng thi Suspended s

b scheduler b qua.

Hm vTaskSuspend() c gi atc v vo trng thi Suspended

Hm vTaskResume() hoc

xvTaskResumeFromISR dng atc v ra khi trng thi Suspended.


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The Ready State

Tc v sn sng chy (vn nm trng thi NotRunning) th trng thiReady

vTaskDelay()void vTaskDelay( portTickType

xTicksToDelay );

Hm vTaskDelay() a tc v vo trng thiBlocked.

Tc v tr li trng thi Ready sauxTicksToDelay ln Systick.


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Example using vTaskDelay

void vTaskFunction( void *pvParameters ){char *pcTaskName;pcTaskName = ( char * ) pvParameters;

/* As per most tasks, this task is implemented in an infinite loop. */for( ;; ){

vPrintString( pcTaskName );

/* In this case a period of 250 milliseconds is being specified. */vTaskDelay( 250 / portTICK_RATE_MS );

}

}





xTaskCreate( vTaskFunction, "Task 2", 1000,

(void*)pcTextForTask2, 2, NULL );vTaskStartScheduler();for( ;; );}


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Task transition


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vTaskDelayUntil() API function

void vTaskDelayUntil( portTickType *pxPreviousWakeTime, portTickTypexTimeIncrement );

vTaskDelayUntil ch chnh xc s lnSystick k t khi tc v chuyn sang trngthi Running trc n ln chuyn sang

trng thi Running k tip

void vTaskFunction( void *pvParameters ){char *pcTaskName;portTickType xLastWakeTime;pcTaskName = ( char * ) pvParameters;

xLastWakeTime = xTaskGetTickCount();


/* Print out the name of this task. */vPrintString( pcTaskName );vTaskDelayUntil( &xLastWakeTime, ( 250 / portTICK_RATE_MS ) );

}}


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Blocking and unblocking task

void vContinuousProcessingTask( void *pvParameters ){

char *pcTaskName;

pcTaskName = ( char * ) pvParameters;for( ;; ){

vPrintString( pcTaskName );}

}

void vPeriodicTask( void *pvParameters ){portTickType xLastWakeTime;

xLastWakeTime = xTaskGetTickCount();


/* Print out the name of this task. */vPrintString( "Periodic task is running\r\n" );

/* The task should execute every 10 milliseconds exactly. */vTaskDelayUntil( &xLastWakeTime, ( 10 / portTICK_RATE_MS ) );

}}


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int main( void ){

xTaskCreate( vContinuousProcessingTask, "Task 1", 1000,(void*)pcTextForTask1, 1, NULL );

xTaskCreate( vContinuousProcessingTask, "Task 2", 1000,(void*)pcTextForTask2, 1, NULL );

/* Create one instance of the periodic task at priority 2. */xTaskCreate( vPeriodicTask, "Task 3", 1000,

(void*)pcTextForPeriodicTask, 2, NULL );

/* Start the scheduler so our tasks start executing. */vTaskStartScheduler();

for( ;; );return 0;}

t1 t2 t3 t4 t5

Periodic

Continuous 1

Continuous 2

IDLE


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IDLE task Idle task c to ra t ng, c u

tin 0.

N c chy khi khng c bt k tc vno c mc u tin cao hn sn sngchy.


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IDLE task hook

Idle task hook l 1 hm c idle taskgi trong mi vng lp ca n.

Idle task hook thng dng : Thc hin cc x l c u tin thp

o thi gian rnh ca h thng

a CPU vo trng thi cng sut thp

IDLE task hook/* Declare a variable that will be incremented by the hook

function. */unsigned long ulIdleCycleCount = 0UL;

/* Idle hook functions MUST be called vApplicationIdleHook(),take no parameters,

and return void. */void vApplicationIdleHook( void ){

/* This hook function does nothing but increment a counter.

*/ulIdleCycleCount++;}


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IDLE task hook

void vTaskFunction( void *pvParameters ){char *pcTaskName;

pcTaskName = ( char * ) pvParameters;


vPrintStringAndNumber( pcTaskName, ulIdleCycleCount );

/* Delay for a period for 250 milliseconds. */vTaskDelay( 250 / portTICK_RATE_MS );

}}

IDLE task hook IDLE task hook khng c block hoc

suspend.

Nu c 1 tc v gi hm vTaskDelete(),IDLE task hook phi quay v idle tasksau 1 khong thi gian v idle task cnhim v t chc li ti nguyn cakernel sau khi c 1 tc v b xa b.


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Change task priority

void vTaskPrioritySet( xTaskHandle pxTask,unsigned portBASE_TYPE uxNewPriority );

(Tham s INCLUDE_vTaskPrioritySet phibng 1 c th dng c hm ny.)

Parameters: pxTask: Handle ca tc v mun c thay i

mc u tin. Nu handle l NULL mc u tin cachnh tc v ang gi hm ny s c set.

uxNewPriority: Mc u tin mi

Query the tasks priorityunsigned portBASE_TYPE uxTaskPriorityGet(

xTaskHandle pxTask );

pxTask: task handle

Nu pxTask l NULL, gi tr tr v s l mc u tinca chnh tc v ang gi hm ny.


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void vTask1( void *pvParameters ){unsigned portBASE_TYPE uxPriority;uxPriority = uxTaskPriorityGet( NULL );

for( ;; ){

/* Print out the name of this task. */vPrintString( "Task1 is running\r\n" );

vPrintString( "About to raise the Task2 priority\r\n" );vTaskPrioritySet( xTask2Handle, ( uxPriority + 1 ) );

}}

void vTask2( void *pvParameters ){unsigned portBASE_TYPE uxPriority;

uxPriority = uxTaskPriorityGet( NULL );

for( ;; ){

vPrintString( "Task2 is running\r\n" );

vTaskPrioritySet( NULL, ( uxPriority - 2 ) );}

}


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/* Declare a variable that is used to hold the handle ofTask2. */

xTaskHandle xTask2Handle;

int main( void ){xTaskCreate( vTask1, "Task 1", 1000, NULL, 2, NULL );xTaskCreate( vTask2, "Task 2", 1000, NULL, 1,

&xTask2Handle );vTaskStartScheduler();

for( ;; );}

Delete a taskvoid vTaskDelete( xTaskHandle

pxTaskToDelete );

Tc v c th xa 1 tc v khc haychnh n.

Ide task s gii phng vng nh cppht cho tc v c xa.


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void vTask1( void *pvParameters ){const portTickType xDelay100ms = 100 / portTICK_RATE_MS;

for( ;; ){

/* Print out the name of this task. */vPrintString( "Task1 is running\r\n" );

xTaskCreate( vTask2, "Task 2", 1000, NULL, 2, &xTask2Handle );vTaskDelay( xDelay100ms );

}}

void vTask2( void *pvParameters )

{

vPrintString( "Task2 is running and aboutto delete itself\r\n" );

vTaskDelete( xTask2Handle );

}


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int main( void ){xTaskCreate( vTask1, "Task 1", 1000, NULL, 1, NULL );

/* Start the scheduler so the tasks start executing. */vTaskStartScheduler();

/* main() should never reach here as the schedulerhas been started. */

for( ;; );}

freeRTOS_taskmanagement

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