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//  ==== Message Queue Management ====
/** 
@addtogroup CMSIS_RTOS_Message Message Queue
@ingroup CMSIS_RTOS
@brief Exchange messages between threads in a FIFO-like operation.
@details 
\b Message \b 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 \b message \b 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:

\image html "MessageQueue.png" "CMSIS-RTOS Message Queue"

Compared to a \ref CMSIS_RTOS_PoolMgmt, 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 \ref osMessageQueuePut, \ref osMessageQueueGet, \ref osMessageQueueGetCapacity,
\ref osMessageQueueGetMsgSize, \ref osMessageQueueGetCount, \ref osMessageQueueGetSpace can be called from
\ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".

@{
*/
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/**
\def osMessageQueueId_t
\details
Returned by:
- \ref osMessageQueueNew
*/

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/** 
\struct osMessageQueueAttr_t
\details
Specifies the following attributes for the \ref osMessageQueueNew function.
*/

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/** 
\fn osMessageQueueId_t osMessageQueueNew (uint32_t msg_count, uint32_t msg_size, const osMessageQueueAttr_t *attr)
\details
The function \ref osMessageQueueNew creates and initializes a message queue object.
The function returns a message queue object identifier or \token{NULL} in case of an error. 

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

The total amount of memory required for the message queue data is at least <code>msg_count * msg_size</code>.
The \em 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 \c msg_size.

\note This function \b cannot be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".

<b>Code Example</b>

Refer to \ref osMessageQueuePut
*/

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/**
\fn const char *osMessageQueueGetName (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueGetName returns the pointer to the name string of the message queue identified by parameter \a
mq_id or \token{NULL} in case of an error.

\note This function may be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn osStatus_t osMessageQueuePut (osMessageQueueId_t mq_id, const void *msg_ptr, uint8_t msg_prio, uint32_t timeout)
\details
The blocking function \b osMessageQueuePut puts the message pointed to by \a msg_ptr into the the message queue specified
by parameter \a mq_id. The parameter \a msg_prio is used to sort message according their priority (higher numbers indicate
a higher priority) on insertion.

The parameter \a 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 \ref ThreadStates "BLOCKED" state. The parameter \ref CMSIS_RTOS_TimeOutValue "timeout"
can have the following values:
 - when \a timeout is \token{0}, the function returns instantly (i.e. try semantics).
 - when \a timeout is set to \b 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 \ref osStatus_t return values:
 - \em osOK: the message has been put into the queue.
 - \em osErrorTimeout: the message could not be put into the queue in the given time (wait-timed semantics).
 - \em osErrorResource: not enough space in the queue (try semantics).
 - \em osErrorParameter: parameter \em mq_id is \token{NULL} or invalid, non-zero timeout specified in an ISR.
 - \em osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

\note May be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines" if the parameter \a timeout is set to
\token{0}.

<b>Code Example:</b>
\code
#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
    }
  }
}
\endcode
*/

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/** 
\fn osStatus_t osMessageQueueGet (osMessageQueueId_t mq_id, void *msg_ptr, uint8_t *msg_prio, uint32_t timeout)
\details
The function \b osMessageQueueGet retrieves a message from the message queue specified by the parameter \a mq_id and saves it
to the buffer pointed to by the parameter \a msg_ptr. The message priority is stored to parameter \a msg_prio if not token{NULL}.

The parameter \a 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 \ref ThreadStates "BLOCKED" state. The parameter
\ref CMSIS_RTOS_TimeOutValue "timeout" can have the following values:
 - when \a timeout is \token{0}, the function returns instantly (i.e. try semantics).
 - when \a timeout is set to \b 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 \ref osStatus_t return values:
 - \em osOK: the message has been retrieved from the queue.
 - \em osErrorTimeout: the message could not be retrieved from the queue in the given time (timed-wait semantics).
 - \em osErrorResource: nothing to get from the queue (try semantics).
 - \em osErrorParameter: parameter \em mq_id is \token{NULL} or invalid, non-zero timeout specified in an ISR.
 - \em osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

\note May be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines" if the parameter \a timeout is set to
\token{0}.

<b>Code Example</b>

Refer to \ref osMessageQueuePut
*/

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/** 
\fn uint32_t osMessageQueueGetCapacity (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueGetCapacity returns the maximum number of messages in the message queue object specified by
parameter \a mq_id or \token{0} in case of an error.

\note This function may be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn uint32_t osMessageQueueGetMsgSize (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueGetMsgSize returns the maximum message size in bytes for the message queue object specified by
parameter \a mq_id or \token{0} in case of an error.

\note This function may be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn uint32_t osMessageQueueGetCount (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueGetCount returns the number of queued messages in the message queue object specified by
parameter \a mq_id or \token{0} in case of an error.

\note This function may be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn uint32_t osMessageQueueGetSpace (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueGetSpace returns the number available slots for messages in the message queue object specified
by parameter \a mq_id or \token{0} in case of an error.

\note This function may be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn osStatus_t osMessageQueueReset (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueReset resets the message queue specified by the parameter \a mq_id.

Possible \ref osStatus_t return values:
 - \em osOK: the message queue has been rest.
 - \em osErrorParameter: parameter \em mq_id is \token{NULL} or invalid.
 - \em osErrorResource: the message queue is in an invalid state.
 - \em osErrorISR: \b osMessageQueueReset cannot be called from interrupt service routines.
 - \em osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

\note This function \b cannot be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/

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/** 
\fn osStatus_t osMessageQueueDelete (osMessageQueueId_t mq_id)
\details
The function \b osMessageQueueDelete deletes a message queue object specified by parameter \a mq_id. It releases internal
memory obtained for message queue handling. After this call, the \a mq_id is no longer valid and cannot be used. The
message queue may be created again using the function \ref osMessageQueueNew.

Possible \ref osStatus_t return values:
 - \em osOK: the message queue object has been deleted.
 - \em osErrorParameter: parameter \em mq_id is \token{NULL} or invalid.
 - \em osErrorResource: the message queue is in an invalid state.
 - \em osErrorISR: \b osMessageQueueDelete cannot be called from interrupt service routines.
 - \em osErrorSafetyClass: the calling thread safety class is lower than the safety class of the specified message queue.

\note This function \b cannot be called from \ref CMSIS_RTOS_ISR_Calls "Interrupt Service Routines".
*/
/// @}

// these struct members must stay outside the group to avoid double entries in documentation
/**
\var osMessageQueueAttr_t::attr_bits
\details
Reserved for future use (must be set to '0' for future compatibility).

\var osMessageQueueAttr_t::cb_mem
\details
Pointer to a memory for the message queue control block object. Refer to \ref CMSIS_RTOS_MemoryMgmt_Manual for more information.

Default: \token{NULL} to use \ref CMSIS_RTOS_MemoryMgmt_Automatic for the message queue control block.

\var osMessageQueueAttr_t::cb_size
\details
The size (in bytes) of memory block passed with \ref cb_mem. Required value depends on the underlying kernel implementation.

Default: \token{0} as the default is no memory provided with \ref cb_mem.

\var osMessageQueueAttr_t::name
\details
Pointer to a constant string with a human readable name (displayed during debugging) of the message queue object.

Default: \token{NULL} no name specified.

\var osMessageQueueAttr_t::mq_mem
\details
Pointer to a memory for the message queue data. Refer to \ref CMSIS_RTOS_MemoryMgmt_Manual for more information.

Default: \token{NULL} to use \ref CMSIS_RTOS_MemoryMgmt_Automatic for the memory pool data.

\var osMessageQueueAttr_t::mq_size
\details
The size (in bytes) of memory block passed with \ref mq_mem. The minimum memory block size is <code>msg_count * msg_size</code> (parameters of the \ref osMessageQueueNew function). The \em 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 \ref mq_mem.
*/
