CMSIS-RTOS RTX  Version 4.51
CMSIS-RTOS RTX: Real-Time Operating System for Cortex-M processor-based devices
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Message Queue Management

Control, send, receive, or wait for messages. More...

Macros

#define osFeature_MessageQ   1
 Message Queues: 1=available, 0=not available.
 
#define osMessageQDef(name, queue_sz, type)
 Create a Message Queue Definition.
 
#define osMessageQ(name)   &os_messageQ_def_##name
 Access a Message Queue Definition.
 

Functions

osMessageQId osMessageCreate (const osMessageQDef_t *queue_def, osThreadId thread_id)
 Create and Initialize a Message Queue.
 
osStatus osMessagePut (osMessageQId queue_id, uint32_t info, uint32_t millisec)
 Put a Message to a Queue.
 
os_InRegs osEvent osMessageGet (osMessageQId queue_id, uint32_t millisec)
 Get a Message or Wait for a Message from a Queue.
 

Description

Message Queue Management functions allow to control, send, receive, or wait for messages. A message can be an integer or pointer value that is send to a thread or interrupt service routine.

MessageQueue.png
CMSIS-RTOS Message Queue

Macro Definition Documentation

#define osFeature_MessageQ   1

A CMSIS-RTOS implementation may support message queues. When the value osFeature_MailQ is 1 message queues are supported. When the value osFeature_MailQ is 0 no message queues are supported.

#define osMessageQ (   name)    &os_messageQ_def_##name

Access to the message queue definition for the function osMessageCreate.

Parameters
namename of the queue
Note
CAN BE CHANGED: The parameter to osMessageQ shall be consistent but the macro body is implementation specific in every CMSIS-RTOS.
#define osMessageQDef (   name,
  queue_sz,
  type 
)

Define the attributes of a message queue created by the function osMessageCreate using osMessageQ.

Parameters
namename of the queue.
queue_szmaximum number of messages in the queue.
typedata type of a single message element (for debugger).
Note
CAN BE CHANGED: The parameter to osMessageQDef shall be consistent but the macro body is implementation specific in every CMSIS-RTOS.

Function Documentation

osMessageQId osMessageCreate ( const osMessageQDef_t queue_def,
osThreadId  thread_id 
)
Parameters
[in]queue_defqueue definition referenced with osMessageQ.
[in]thread_idthread ID (obtained by osThreadCreate or osThreadGetId) or NULL.
Returns
message queue ID for reference by other functions or NULL in case of error.
Note
MUST REMAIN UNCHANGED: osMessageCreate shall be consistent in every CMSIS-RTOS.

Create and initialize a message queue.

Example:

#include "cmsis_os.h"
osThreadId tid_thread1; // ID for thread 1
osThreadId tid_thread2; // for thread 2
typedef struct { // Message object structure
float voltage; // AD result of measured voltage
float current; // AD result of measured current
int counter; // A counter value
} T_MEAS;
osPoolDef(mpool, 16, T_MEAS); // Define memory pool
osPoolId mpool;
osMessageQDef(MsgBox, 16, T_MEAS); // Define message queue
osMessageQId MsgBox;
void send_thread (void const *argument); // forward reference
void recv_thread (void const *argument); // forward reference
// Thread definitions
osThreadDef(send_thread, osPriorityNormal, 1, 0);
osThreadDef(recv_thread, osPriorityNormal, 1, 2000);
/*
Thread 1: Send thread
*/
void send_thread (void const *argument) {
T_MEAS *mptr;
mptr = osPoolAlloc(mpool); // Allocate memory for the message
mptr->voltage = 223.72; // Set the message content
mptr->current = 17.54;
mptr->counter = 120786;
osMessagePut(MsgBox, (uint32_t)mptr, osWaitForever); // Send Message
osDelay(100);
mptr = osPoolAlloc(mpool); // Allocate memory for the message
mptr->voltage = 227.23; // Prepare a 2nd message
mptr->current = 12.41;
mptr->counter = 170823;
osMessagePut(MsgBox, (uint32_t)mptr, osWaitForever); // Send Message
osThreadYield(); // Cooperative multitasking
// We are done here, exit this thread
}
/*
Thread 2: Receive thread
*/
void recv_thread (void const *argument) {
T_MEAS *rptr;
osEvent evt;
for (;;) {
evt = osMessageGet(MsgBox, osWaitForever); // wait for message
if (evt.status == osEventMessage) {
rptr = evt.value.p;
printf ("\nVoltage: %.2f V\n", rptr->voltage);
printf ("Current: %.2f A\n", rptr->current);
printf ("Number of cycles: %d\n", rptr->counter);
osPoolFree(mpool, rptr); // free memory allocated for message
}
}
}
void StartApplication (void) {
mpool = osPoolCreate(osPool(mpool)); // create memory pool
MsgBox = osMessageCreate(osMessageQ(MsgBox), NULL); // create msg queue
tid_thread1 = osThreadCreate(osThread(send_thread), NULL);
tid_thread2 = osThreadCreate(osThread(recv_thread), NULL);
:
}
osEvent osMessageGet ( osMessageQId  queue_id,
uint32_t  millisec 
)
Parameters
[in]queue_idmessage queue ID obtained with osMessageCreate.
[in]millisectimeout value or 0 in case of no time-out.
Returns
event information that includes status code.
Note
MUST REMAIN UNCHANGED: osMessageGet shall be consistent in every CMSIS-RTOS.

Suspend the execution of the current RUNNING thread until a message arrives. When a message is already in the queue, the function returns instantly with the message information. When millisec is 0, the function returns instantly with status osOK. Otherwise the thread is put into the state WAITING. When millisec is set to osWaitForever the function will wait for an infinite time until a message arrives.

Note
The parameter millisec must be 0 for using this function in an ISR.

Status and Error Codes

  • osOK: no message is available in the queue and no timeout was specified.
  • osEventTimeout: no message has arrived during the given timeout period.
  • osEventMessage: message received, value.p contains the pointer to message.
  • osErrorParameter: a parameter is invalid or outside of a permitted range.
osStatus osMessagePut ( osMessageQId  queue_id,
uint32_t  info,
uint32_t  millisec 
)
Parameters
[in]queue_idmessage queue ID obtained with osMessageCreate.
[in]infomessage information.
[in]millisectimeout value or 0 in case of no time-out.
Returns
status code that indicates the execution status of the function.
Note
MUST REMAIN UNCHANGED: osMessagePut shall be consistent in every CMSIS-RTOS.

Put the message info in a message queue specified by queue_id. When the message queue is full, the system retries for a specified time with millisec. In this case, the tread is put into the state WAITING. When millisec is set to osWaitForever, the function will wait for an infinite time until a message queue slot becomes available.

Note
The parameter millisec must be 0 for using this function in an ISR.

Status and Error Codes

  • osOK: the message is put into the queue.
  • osErrorResource: no memory in the queue was available.
  • osErrorTimeoutResource: no memory in the queue was available during the given time limit.
  • osErrorParameter: a parameter is invalid or outside of a permitted range.