FreeRTOS Course - Queue Management

Introduction to FreeRTOS V6.0.5

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Introduction to FreeRTOS V6.0.5 Amr Ali Abdel-Naby@2010

About Me
Graduated 2004
ECE, ASU: 5 yrs distinction
6+ years in embedded systems development
SDLC, Apps, MW, DD, Porting, ...
4+ years in SW engineering
PSP, CMMI, Systematic reuse, ...
4+ years in SW testing
IBM certified, ISTQB certified, ...

Copyright
Materials in this course is the property of Amr Ali Abdel-Naby.
Reproduction or transmission of the materials outside [Customer Name] in any manner without the copyright owner permission is a law violation.
[Customer Name] is free to use this material as is within its head quarters for noncommercial uses.
Snapshots or trademarks used are retained to their original owners.

Course Objectives
After completing this course, you will:
Understand what is FreeRTOS
Experience different FreeRTOS services and APIs
Understand the porting process of FreeRTOS

Course Notes
I assume you are familiar with RTOS concepts.
I assume you know C.
I assume you know 80x86 architecture and assembly.
Ask any time.

Course References
http://www.freertos.org

Outline
Introduction to FreeRTOS
Lab 0: Getting Started
Kernel Structure
Lab 1: Kernel Structure
Task Management
Lab 2: Task Management
Queue Management
Lab 3: Queue Management
Semaphore/Mutex Management
Lab 4: Semaphore/Mutex Management
Co-routine Management
Lab 5: Co-routine Management
Advanced Features
Lab 6: Advanced Features
Porting FreeRTOS
Lab 7: Porting FreeRTOS
Amr Ali Abdel-Naby@2010 Introduction to FreeRTOS V6.0.5

Queues
Task-safe FIFO buffers
Fixed size messages
Defined during creation
Messages placed by copy not reference.
You can copy message reference instead.
Application programmer responsibility
Queues are blocking but to a timeout.
Amr Ali Abdel-Naby@2010 Introduction to FreeRTOS V6.0.5 Message ISR Task Task

More About Queues
Some of their APIs are macros that point to queues’ implementation APIs.
Same queues’ implementation APIs are used to implement semaphores/mutexes.
Queues and semaphores/mutexes APIs are inter-operable.
You should be careful if your are going to do this.

Queue Management APIs
They fall under 4 categories:
Amr Ali Abdel-Naby@2010 Introduction to FreeRTOS V6.0.5 Creation xQueueCreate vQueueDelete Fully Featured xQueueSend xQueueSendToBack xQueueSendToFront xQueueReceive xQueuePeek uxQueueMessagesWaiting Light Weight xQueueSendFromISR xQueueSendToBackFromISR xQueueSendToFrontFromISR xQueueReceiveFromISR uxQueueMessagesWaitingFromISR xQueueIsQueueEmptyFromISR xQueueIsQueueFullFromISR Alternative xQueueAltSendToBack xQueueAltSendToFront xQueueAltReceive xQueueAltPeek

Creating a Queue, xQueueCreate
xQueueHandle xQueueCreate(unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize)
uxQueueLength: The maximum number of items that the queue can contain
uxItemSize: The number of bytes each message in the queue will require
Each message posted on the queue must be the same size.
Return value:
Handle to the newly created queue on success
NULL on failure

Deleting a Queue, vQueueDelete
void vQueueDelete(xQueueHandle xQueue)
xQueue: A handle to the queue to be deleted

Sending a Message, xQueueSend
portBASE_TYPE xQueueSend( xQueueHandle xQueue, const void * pvItemToQueue, portTickType xTicksToWait)
xQueue: The handle to the queue on which the message is to be posted.
pvItemToQueue: A pointer to the message that is to be placed on the queue
Message size should match size defined during creation.
xTicksToWait: The maximum amount of time the task should block waiting for space to become available on the queue
Return value:
pdTRUE if the item was successfully posted
Otherwise errQUEUE_FULL

Sending a Message to Queue End, xQueueSendToBack
portBASE_TYPE xQueueSendToBack(xQueueHandle xQueue, const void * pvItemToQueue, portTickType xTicksToWait)
= xQueueSend
Newer version that will be used in future versions of FreeRTOS

Sending a Message to Queue Front, xQueueSendToFront
portBASE_TYPE xQueueSendToFront(xQueueHandle xQueue, const void * pvItemToQueue, portTickType xTicksToWait)
= xQueueSend but with LIFO order

Destructive Receiving of a Message, xQueueReceive
portBASE_TYPE xQueueReceive(xQueueHandle xQueue, void * pvBuffer, portTickType xTicksToWait)
pxQueue: The handle to the queue from which the message is to be received
pvBuffer: Pointer to the buffer into which the received message will be copied
Size defined during creation will be used
Its size should be adequate.
xTicksToWait: The maximum amount of time the task should block waiting for a message to become available on the queue
Return value:
pdTRUE if the item was successfully posted
Otherwise pdFALSE

Non-Destructive Receiving, xQueuePeek
portBASE_TYPE xQueuePeek(xQueueHandle xQueue, void * pvBuffer, portTickType xTicksToWait)
= xQueueReceive but non-destructive

Getting Number of Messages in a Queue, uxQueueMessagesWaiting
unsigned portBASE_TYPE uxQueueMessagesWaiting(const xQueueHandle xQueue)
xQueue: A handle to the queue being queried
Return value: The number of messages available in the queue

Sending a Message from ISR, xQueueSendFromISR
portBASE_TYPE xQueueSendFromISR(xQueueHandle pxQueue, const void * pvItemToQueue, portBASE_TYPE * pxHigherPriorityTaskWoken)
= xQueueSend but used within ISRs
pxHigherPriorityTaskWoken: Is set to pdTRUE if sending caused a higher priority task to unblock
A context switch is needed after ISR exits.

Sending a Message to Queue End from ISR, xQueueSendToBackFromISR
portBASE_TYPE xQueueSendToBackFromISR(xQueueHandle pxQueue, const void * pvItemToQueue, portBASE_TYPE *pxHigherPriorityTaskWoken)
= xQueueSendFromISR

Sending a Message to Queue Front from ISR, xQueueSendToFrontFrom ISR
portBASE_TYPE xQueueSendToFrontFromISR(xQueueHandle pxQueue, const void *pvItemToQueue, portBASE_TYPE * pxHigherPriorityTaskWoken)
= xQueueSendFromISR but with LIFO order

Destructive Receiving of a Message From ISR, xQueueReceiveFromISR
portBASE_TYPE xQueueReceiveFromISR(xQueueHandle pxQueue, void * pvBuffer, portBASE_TYPE * pxTaskWoken)
= xQueueReceive but used within ISRs
pxTaskWoken : Is set to pdTRUE if receiving caused a higher priority task to unblock
A context switch is needed after ISR exits.

Getting Number of Messages in a Queue from ISR, uxQueueMessagesWaitingFromISR
unsigned portBASE_TYPE uxQueueMessagesWaitingFromISR( const xQueueHandle pxQueue )
= uxQueueMessagesWaiting but used within ISRs

Checking Queue Emptiness from ISR, xQueueIsQueueEmptyFromISR
signed portBASE_TYPE xQueueIsQueueEmptyFromISR( const xQueueHandle pxQueue)
pxQueue: A handle to the queue being queried
Return value:
!0 if empty
0 if not empty

Checking Queue Fullness from ISR, xQueueIsQueueFullFromISR
signed portBASE_TYPE xQueueIsQueueFullFromISR(const xQueueHandle pxQueue)
pxQueue: A handle to the queue being queried
Return value:
!0 if full
0 if not full

Alternative Sending a Message to Queue End, xQueueSendToBack
portBASE_TYPE xQueueAltSendToBack(xQueueHandle xQueue, const void * pvItemToQueue, portTickType xTicksToWait)
= xQueueSendToBack but with alternative implementation

Alternative Sending a Message to Queue Front, xQueueAltSendToFront
portBASE_TYPE xQueueAltSendToFront(xQueueHandle xQueue, const void * pvItemToQueue, portTickType xTicksToWait)
= xQueueSendToFront but with alternative implementation

AlternativeDestructive Receiving of a Message, xQueueAltReceive
portBASE_TYPE xQueueAltReceive(xQueueHandle xQueue, void * pvBuffer, portTickType xTicksToWait)
= xQueueAltReceive but with alternative implementation

Alternative Non-Destructive Receiving, xQueueAltPeek
portBASE_TYPE xQueueAltPeek(xQueueHandle xQueue, void * pvBuffer, portTickType xTicksToWait)
xQueueAltPeek but with alternative implementation

Outline
Introduction to FreeRTOS
Lab 0: Getting Started
Kernel Structure
Lab 1: Kernel Structure
Task Management
Lab 2: Task Management
Queue Management
Lab 3: Queue Management
Semaphore/Mutex Management
Lab 4: Semaphore/Mutex Management
Co-routine Management
Lab 5: Co-routine Management
Advanced Features
Lab 6: Advanced Features
Porting FreeRTOS
Lab 7: Porting FreeRTOS

Lab3: Queue Management
Please follow the instructions in the lab handout

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FreeRTOS Course - Queue Management

by amraldo on Jul 03, 2010

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