Liteos message queuing

Catalog

• Preface
  • link
  • Reference resources
• Draft notes
• Basic concepts
• Queue operation mechanism
• How queues work
• Message queue transmission mode
• Blocking mechanism of message queue
  • Out of line jam
  • Blocking in the queue
• Task related function
• Task development process
• matters needing attention *
• actual combat

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Preface

link

• LiteOS Source link
• common problem
• Huawei developer community
• Huawei LiteOS The official tutorial
• my gitee-LiteOS-mcu

Reference resources

• Wildfire
• The link above

Draft notes

• I'm a little busy with my work recently , Far away? Reading delayed. Ha ha

Basic concepts

• queue also called Message queue

  • It is a data structure commonly used for inter task communication
  • Ability to receive messages of variable length from tasks or interrupts
  • According to API Choose whether the delivery message is stored in your own space
    • That is The data transfer still Address
  • The task can read messages from the queue
    • When the message in the queue is empty
      • Pending read task
    • When there are new messages in the queue
      • The pending read task is awakened
      • And deal with new news .

• LiteOS Queue properties

  • Messages are queued first in, first out （FIFO）, Support asynchronous read-write mode
  • Both read and write queues support timeout mechanisms
  • The type of message to be sent shall be agreed by both parties , Different lengths can be allowed （ No more than the maximum number of queue nodes ） news
  • A task can receive and send messages from any message queue
  • Multiple tasks can receive and send messages from the same message queue
  • When the queue is finished , If it is dynamically applied memory , You need to recycle by freeing memory functions .

Queue operation mechanism

• Queue control block
  • usReadWriteableCnt : The number of messages that can be read or written
  • stReadWriteList : Read or write message task wait list
  • usQueueState : Two kinds of state
    • OS_QUEUE_UNUSED ： Not used
    • OS_QUEUE_INUSED ： Used

/**
  * @ingroup los_queue
  * Queue information block structure
  */
typedef struct tagQueueCB
{
    UINT8       *pucQueue;                              /**< Pointer to a queue handle */
    UINT16      usQueueState;                           /**< Queue state */
    UINT16      usQueueLen;                             /**< Queue length */
    UINT16      usQueueSize;                            /**< Node size     */
    UINT16      usQueueID;                              /**< usQueueID         */
    UINT16      usQueueHead;                            /**< Node head       */
    UINT16      usQueueTail;                            /**< Node tail       */
    UINT16      usReadWriteableCnt[2];       /**< Count of readable or writable resources, 0:readable, 1:writable */
    LOS_DL_LIST stReadWriteList[2];          /**< Pointer to the linked list to be read or written, 0:readlist, 1:writelist  */
    LOS_DL_LIST stMemList;                              /**< Pointer to the memory linked list */
} QUEUE_CB_S;
/* queue state */
/**
  *  @ingroup los_queue
  *  Message queue state: not in use.
  */
#define OS_QUEUE_UNUSED                 0

/**
  *  @ingroup los_queue
  *  Message queue state: used.
  */
#define OS_QUEUE_INUSED     1

How queues work

• Create a queue

  • Pass in The queue length and Message node size
  • Open up the corresponding memory space
  • return queue ID.

• In line Header node Head and Message tail node Tail

  • Head Indicates the starting position of the occupied message in the queue
  • Tail Indicates the starting position of the idle message in the queue
  • Both of them adopt the way of rewinding

• usReadWriteableCnt[0] Determine whether it is readable

• usReadWriteableCnt[1] Determine whether it is writable

• When deleting a queue

  • According to the incoming queue ID Find the corresponding queue
  • Set the queue state to unused
  • Free up the space occupied by the original queue
  • The corresponding queue control header is set to the initial state .

• The illustration ：

• 

Message queue transmission mode

• LiteOS There are two ways to transmit messages

  1. Address mode
     1. advantage ： Efficient
     2. shortcoming ： Modify source file , The corresponding content of the message will also be modified
  2. Copy mode
     1. advantage ： Data security , It's copying content directly into the message
     2. shortcoming ： Efficiency is relative Address It's lower

• Users can choose different ways according to their needs

  • Main reference data size And Data importance To measure

Blocking mechanism of message queue

• Interrupt with blocking mechanism is not allowed API, So the interruption , The blocking values are taken as 0
• LiteOS The blocking mechanism has been implemented , Users can use it directly

Out of line jam

• Three ways ： It mainly refers to whether there are messages in the queue
  • Don't wait for ：0
    • When reading a message , Inside the queue
      • News , Normal read
      • No news , You don't wait , Directly execute the following code
  • Wait for a limited time ：
    • Within the prescribed time , In the message queue
      • News , Normal read ,
      • No news , Is waiting for
    • Overtime
      • Then directly execute the following code
  • Wait forever ：LOS_WAIT_FOREVER
    • When reading a message
      • News , Normal read
      • No news , Have been waiting for , Until there's a message in the queue

Blocking in the queue

• Three ways ： It mainly refers to whether the messages in the queue are full
  • Don't wait for ：0
    • When writing a message
      • The queue is under , The normal writing
      • The queue is full , You don't wait , Directly execute the following code
  • Wait for a limited time ：
    • When writing a message
      • The queue is under , The normal writing
      • The queue is full , Wait for a limited time , Wait until the queue is full and write
    • Overtime
      • Then directly execute the following code
  • Wait forever ：LOS_WAIT_FOREVER
    • When writing a message
      • The queue is under , The normal writing
      • The queue is full , Have been waiting for , Until the queue is not full

Task related function

The interface name	describe
LOS_QueueCreate	Create a message
LOS_QueueRead	Read the data in the specified queue .（buff It contains the address of the queue node ）
LOS_QueueWrite	Write data to the specified queue .（ What is written to the queue node is buff The address of ）
LOS_QueueReadCopy	Read the data in the specified queue .（buff It stores the data in the queue node ）（ Reserved interface ）
LOS_QueueWriteCopy	Write data to the specified queue .（ What is written to the queue node is buff Data in ）（ Reserved interface ）
LOS_QueueWriteHead	Write data to the head of the specified queue
LOS_QueueDelete	Delete a specified queue
LOS_QueueInfoGet	Get the specified queue information

The use of each function can see the source code or routine

Task development process

• Not copy The way ( copy In the same way )
  1. Create a message queue LOS_QueueCreate.
  2. Once created , You can get the message queue ID value .
  3. Write queue operation function LOS_QueueWrite.
  4. Read queue operation function LOS_QueueRead.
  5. Get queue information function LOS_QueueInfoGet.
  6. To delete a queue LOS_QueueDelete.

matters needing attention *

1. The number of queue resources that can be configured by the system
   • Refer to The total number of queue resources of the whole system
   • Not the number of users can use .
   • for example ：
     • The system software timer takes up more than one queue resource
     • Then the queue resources that the system can configure will be reduced by one .
2. call LOS_QueueCreate The queue name passed in by function is not used temporarily , As a future reserved parameter .
3. The input parameter in the queue interface function uwTimeOut It means relative time .
4. LOS_QueueReadCopy and LOS_QueueWriteCopy It's a set of interfaces
5. LOS_QueueRead and LOS_QueueWrite It's a set of interfaces , Two sets of interfaces need to be used together .
6. Whereas LOS_QueueWrite and LOS_QueueRead The actual operation of this group of interfaces is data address , The user must make sure to call LOS_QueueRead The obtained pointer points to the memory area during the read queue Not modified or released by exception , Otherwise, it may lead to unpredictable consequences .

• When using address mode , It must be ensured that the content of the address has not been modified , Local variables are not recommended
• When using address mode , It must be ensured that the content of the address has not been modified , Local variables are not recommended
• When using address mode , It must be ensured that the content of the address has not been modified , Local variables are not recommended

actual combat

Actual address