Exchange messages between threads in a FIFO-like operation. More...

Data Structures
struct	osMessageQueueAttr_t
	Attributes structure for message queue. More...

Functions
osMessageQueueId_t	osMessageQueueNew (uint32_t msg_count, uint32_t msg_size, const osMessageQueueAttr_t *attr)
	Create and Initialize a Message Queue object. More...

const char *	osMessageQueueGetName (osMessageQueueId_t mq_id)
	Get name of a Message Queue object. More...

osStatus_t	osMessageQueuePut (osMessageQueueId_t mq_id, const void *msg_ptr, uint8_t msg_prio, uint32_t timeout)
	Put a Message into a Queue or timeout if Queue is full. More...

osStatus_t	osMessageQueueGet (osMessageQueueId_t mq_id, void msg_ptr, uint8_t msg_prio, uint32_t timeout)
	Get a Message from a Queue or timeout if Queue is empty. More...

uint32_t	osMessageQueueGetCapacity (osMessageQueueId_t mq_id)
	Get maximum number of messages in a Message Queue. More...

uint32_t	osMessageQueueGetMsgSize (osMessageQueueId_t mq_id)
	Get maximum message size in a Message Queue. More...

uint32_t	osMessageQueueGetCount (osMessageQueueId_t mq_id)
	Get number of queued messages in a Message Queue. More...

uint32_t	osMessageQueueGetSpace (osMessageQueueId_t mq_id)
	Get number of available slots for messages in a Message Queue. More...

osStatus_t	osMessageQueueReset (osMessageQueueId_t mq_id)
	Reset a Message Queue to initial empty state. More...

osStatus_t	osMessageQueueDelete (osMessageQueueId_t mq_id)
	Delete a Message Queue object. More...

Description

Message passing is another basic communication model between threads. In the message passing model, one thread sends data explicitly, while another thread receives it. The operation is more like some kind of I/O rather than a direct access to information to be shared. In CMSIS-RTOS, this mechanism is called a message queue. The data is passed from one thread to another in a FIFO-like operation. Using message queue functions, you can control, send, receive, or wait for messages. The data to be passed can be of integer or pointer type:

CMSIS-RTOS Message Queue

Compared to a Memory Pool, message queues are less efficient in general, but solve a broader range of problems. Sometimes, threads do not have a common address space or the use of shared memory raises problems, such as mutual exclusion.

Note: The functions osMessageQueuePut, osMessageQueueGet, osMessageQueueGetCapacity, osMessageQueueGetMsgSize, osMessageQueueGetCount, osMessageQueueGetSpace can be called from Interrupt Service Routines.; Refer to Message Queue Configuration for RTX5 configuration options.

Data Structure Documentation

struct osMessageQueueAttr_t

Specifies the following attributes for the osMessageQueueNew function.

Data Fields
const char *	name	name of the message queue Pointer to a constant string with a human readable name (displayed during debugging) of the message queue object. Default: NULL no name specified.
uint32_t	attr_bits	attribute bits Reserved for future use (must be set to '0' for future compatibility).
void *	cb_mem	memory for control block Pointer to a memory for the message queue control block object. Refer to Static Object Memory for more information. Default: NULL to use Automatic Dynamic Allocation for the message queue control block.
uint32_t	cb_size	size of provided memory for control block The size (in bytes) of memory block passed with cb_mem. For RTX, the minimum value is defined with osRtxMessageQueueCbSize (higher values are permitted). Default: 0 as the default is no memory provided with cb_mem.
void *	mq_mem	memory for data storage Pointer to a memory for the message queue data. Refer to Static Object Memory for more information. Default: NULL to use Automatic Dynamic Allocation for the memory pool data.
uint32_t	mq_size	size of provided memory for data storage The size (in bytes) of memory block passed with mq_mem. The minimum memory block size is `msg_count * msg_size` (parameters of the osMessageQueueNew function). The msg_size is rounded up to a double even number to ensure 32-bit alignment of the memory blocks. Default: 0 as the default is no memory provided with mq_mem.

Function Documentation

osMessageQueueId_t osMessageQueueNew	(	uint32_t	msg_count,
		uint32_t	msg_size,
		const osMessageQueueAttr_t *	attr
	)

Parameters

[in]	msg_count	maximum number of messages in queue.
[in]	msg_size	maximum message size in bytes.
[in]	attr	message queue attributes; NULL: default values.

Returns: message queue ID for reference by other functions or NULL in case of error.

The function osMessageQueueNew creates and initializes a message queue object. The function returns a message queue object identifier or NULL in case of an error.

The function can be called after kernel initialization with osKernelInitialize. It is possible to create message queue objects before the RTOS kernel is started with osKernelStart.

The total amount of memory required for the message queue data is at least msg_count * msg_size. The msg_size is rounded up to a double even number to ensure 32-bit alignment of the memory blocks.

The memory blocks allocated from the message queue have a fixed size defined with the parameter msg_size.

Note: This function cannot be called from Interrupt Service Routines.

Code Example

Refer to osMessageQueuePut

const char * osMessageQueueGetName ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: name as null-terminated string.

The function osMessageQueueGetName returns the pointer to the name string of the message queue identified by parameter mq_id or NULL in case of an error.

Note: This function may be called from Interrupt Service Routines.

osStatus_t osMessageQueuePut	(	osMessageQueueId_t	mq_id,
		const void *	msg_ptr,
		uint8_t	msg_prio,
		uint32_t	timeout
	)

Parameters

[in]	mq_id	message queue ID obtained by osMessageQueueNew.
[in]	msg_ptr	pointer to buffer with message to put into a queue.
[in]	msg_prio	message priority.
[in]	timeout	Timeout Value or 0 in case of no time-out.

Returns: status code that indicates the execution status of the function.

The blocking function osMessageQueuePut puts the message pointed to by msg_ptr into the the message queue specified by parameter mq_id. The parameter msg_prio is used to sort message according their priority (higher numbers indicate a higher priority) on insertion.

The parameter timeout specifies how long the system waits to put the message into the queue. While the system waits, the thread that is calling this function is put into the BLOCKED state. The parameter timeout can have the following values:

when timeout is 0, the function returns instantly (i.e. try semantics).
when timeout is set to osWaitForever the function will wait for an infinite time until the message is delivered (i.e. wait semantics).
all other values specify a time in kernel ticks for a timeout (i.e. timed-wait semantics).

Possible osStatus_t return values:

osOK: the message has been put into the queue.
osErrorTimeout: the message could not be put into the queue in the given time (wait-timed semantics).
osErrorResource: not enough space in the queue (try semantics).
osErrorParameter: parameter mq_id is NULL or invalid, non-zero timeout specified in an ISR.
osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

Note: May be called from Interrupt Service Routines if the parameter timeout is set to 0.

Code Example:

#include "cmsis_os2.h"                          // CMSIS RTOS header file
 
/*----------------------------------------------------------------------------
 *      Message Queue creation & usage
 *---------------------------------------------------------------------------*/
 
#define MSGQUEUE_OBJECTS 16                     // number of Message Queue Objects
 
typedef struct {                                // object data type
  uint8_t Buf[32];
  uint8_t Idx;
} MSGQUEUE_OBJ_t;
 
osMessageQueueId_t mid_MsgQueue;                // message queue id
 
osThreadId_t tid_Thread_MsgQueue1;              // thread id 1
osThreadId_t tid_Thread_MsgQueue2;              // thread id 2
 
void Thread_MsgQueue1 (void *argument);         // thread function 1
void Thread_MsgQueue2 (void *argument);         // thread function 2
 
int Init_MsgQueue (void) {
 
  mid_MsgQueue = osMessageQueueNew(MSGQUEUE_OBJECTS, sizeof(MSGQUEUE_OBJ_t), NULL);
  if (mid_MsgQueue == NULL) {
    ; // Message Queue object not created, handle failure
  }
 
  tid_Thread_MsgQueue1 = osThreadNew(Thread_MsgQueue1, NULL, NULL);
  if (tid_Thread_MsgQueue1 == NULL) {
    return(-1);
  }
  tid_Thread_MsgQueue2 = osThreadNew(Thread_MsgQueue2, NULL, NULL);
  if (tid_Thread_MsgQueue2 == NULL) {
    return(-1);
  }
 
  return(0);
}
 
void Thread_MsgQueue1 (void *argument) {
  MSGQUEUE_OBJ_t msg;
 
  while (1) {
    ; // Insert thread code here...
    msg.Buf[0] = 0x55U;                                         // do some work...
    msg.Idx    = 0U;
    osMessageQueuePut(mid_MsgQueue, &msg, 0U, 0U);
    osThreadYield();                                            // suspend thread
  }
}
 
void Thread_MsgQueue2 (void *argument) {
  MSGQUEUE_OBJ_t msg;
  osStatus_t status;
 
  while (1) {
    ; // Insert thread code here...
    status = osMessageQueueGet(mid_MsgQueue, &msg, NULL, 0U);   // wait for message
    if (status == osOK) {
      ; // process data
    }
  }
}

osStatus_t osMessageQueueGet	(	osMessageQueueId_t	mq_id,
		void *	msg_ptr,
		uint8_t *	msg_prio,
		uint32_t	timeout
	)

Parameters

[in]	mq_id	message queue ID obtained by osMessageQueueNew.
[out]	msg_ptr	pointer to buffer for message to get from a queue.
[out]	msg_prio	pointer to buffer for message priority or NULL.
[in]	timeout	Timeout Value or 0 in case of no time-out.

Returns: status code that indicates the execution status of the function.

The function osMessageQueueGet retrieves a message from the message queue specified by the parameter mq_id and saves it to the buffer pointed to by the parameter msg_ptr. The message priority is stored to parameter msg_prio if not token{NULL}.

The parameter timeout specifies how long the system waits to retrieve the message from the queue. While the system waits, the thread that is calling this function is put into the BLOCKED state. The parameter timeout can have the following values:

when timeout is 0, the function returns instantly (i.e. try semantics).
when timeout is set to osWaitForever the function will wait for an infinite time until the message is retrieved (i.e. wait semantics).
all other values specify a time in kernel ticks for a timeout (i.e. timed-wait semantics).

Possible osStatus_t return values:

osOK: the message has been retrieved from the queue.
osErrorTimeout: the message could not be retrieved from the queue in the given time (timed-wait semantics).
osErrorResource: nothing to get from the queue (try semantics).
osErrorParameter: parameter mq_id is NULL or invalid, non-zero timeout specified in an ISR.
osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

Note: May be called from Interrupt Service Routines if the parameter timeout is set to 0.

Code Example

Refer to osMessageQueuePut

uint32_t osMessageQueueGetCapacity ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: maximum number of messages.

The function osMessageQueueGetCapacity returns the maximum number of messages in the message queue object specified by parameter mq_id or 0 in case of an error.

Note: This function may be called from Interrupt Service Routines.

uint32_t osMessageQueueGetMsgSize ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: maximum message size in bytes.

The function osMessageQueueGetMsgSize returns the maximum message size in bytes for the message queue object specified by parameter mq_id or 0 in case of an error.

Note: This function may be called from Interrupt Service Routines.

uint32_t osMessageQueueGetCount ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: number of queued messages.

The function osMessageQueueGetCount returns the number of queued messages in the message queue object specified by parameter mq_id or 0 in case of an error.

Note: This function may be called from Interrupt Service Routines.

uint32_t osMessageQueueGetSpace ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: number of available slots for messages.

The function osMessageQueueGetSpace returns the number available slots for messages in the message queue object specified by parameter mq_id or 0 in case of an error.

Note: This function may be called from Interrupt Service Routines.

osStatus_t osMessageQueueReset ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: status code that indicates the execution status of the function.

The function osMessageQueueReset resets the message queue specified by the parameter mq_id.

Possible osStatus_t return values:

osOK: the message queue has been rest.
osErrorParameter: parameter mq_id is NULL or invalid.
osErrorResource: the message queue is in an invalid state.
osErrorISR: osMessageQueueReset cannot be called from interrupt service routines.
osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

Note: This function cannot be called from Interrupt Service Routines.

osStatus_t osMessageQueueDelete ( osMessageQueueId_t mq_id )

Parameters

[in] mq_id message queue ID obtained by osMessageQueueNew.

Returns: status code that indicates the execution status of the function.

The function osMessageQueueDelete deletes a message queue object specified by parameter mq_id. It releases internal memory obtained for message queue handling. After this call, the mq_id is no longer valid and cannot be used. The message queue may be created again using the function osMessageQueueNew.

Possible osStatus_t return values:

osOK: the message queue object has been deleted.
osErrorParameter: parameter mq_id is NULL or invalid.
osErrorResource: the message queue is in an invalid state.
osErrorISR: osMessageQueueDelete cannot be called from interrupt service routines.
osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

Note: This function cannot be called from Interrupt Service Routines.

Data Structures

Functions

Description

Data Structure Documentation

Function Documentation