Mutex Management

Synchronize thread execution with a Mutex. More...

Macros
#define	osMutexDef(name)
	Define a Mutex.
#define	osMutex(name)   &os_mutex_def_##name
	Access a Mutex definition.

Functions
osMutexId	osMutexCreate (const osMutexDef_t *mutex_def)
	Create and Initialize a Mutex object.
osStatus	osMutexWait (osMutexId mutex_id, uint32_t millisec)
	Wait until a Mutex becomes available.
osStatus	osMutexRelease (osMutexId mutex_id)
	Release a Mutex that was obtained by osMutexWait.
osStatus	osMutexDelete (osMutexId mutex_id)
	Delete a Mutex that was created by osMutexCreate.

Description

The Mutex Management function group is used to synchronize the execution of threads. This is for example used to protect access to a shared resource, for example a shared memory image.

Note

Mutex Management functions cannot be called from interrupt service routines (ISR).

CMSIS-RTOS Mutex

Macro Definition Documentation

#define osMutex

(

name

)

&os_mutex_def_##name

Access to mutex object for the functions osMutexCreate.

Parameters

name	name of the mutex object.

#define osMutexDef

(

name

)

Define a mutex object that is referenced by osMutex.

Parameters

name	name of the mutex object.

Function Documentation

osMutexId osMutexCreate

(

const osMutexDef_t *

mutex_def

)

Parameters

[in]

mutex_def

mutex definition referenced with osMutex.

Returns

mutex ID for reference by other functions or NULL in case of error.

Create and initialize a Mutex object.

Note

Cannot be called from Interrupt Service Routines.

Example

#include "cmsis_os.h"
  
osMutexDef (MutexIsr);                                     // Mutex name definition
  
void CreateMutex (void)  {
osMutexId mutex_id;   
 
  mutex_id = osMutexCreate  (osMutex (MutexIsr));
  if (mutex_id != NULL)  {
    // Mutex object created
  }   
}

osStatus osMutexDelete

(

osMutexId

mutex_id

)

Parameters

[in]

mutex_id

mutex ID obtained by osMutexCreate.

Returns

status code that indicates the execution status of the function.

Delete a Mutex object. The function releases internal memory obtained for Mutex handling. After this call the mutex_id is no longer valid and cannot be used. The Mutex may be created again using the function osMutexCreate.

Status and Error Codes

• osOK: the mutex object has been deleted.
• osErrorISR: osMutexDelete cannot be called from interrupt service routines.
• osErrorResource: all tokens have already been released.
• osErrorParameter: the parameter mutex_id is incorrect.

Note

Cannot be called from Interrupt Service Routines.

Example

#include "cmsis_os.h"
  
osMutexDef (MutexIsr);                                     // Mutex name definition 
osMutexId mutex_id;                                        // Mutex id populated by the function CreateMutex()
osMutexId CreateMutex (void);                              // function prototype that creates the Mutex
 
void DeleteMutex (osMutexId mutex_id)  {
osStatus status;
  
  if (mutex_id != NULL)  {
    status = osMutexDelete(mutex_id);
    if (status != osOK)  {
      // handle failure code
    }
  }
}

osStatus osMutexRelease

(

osMutexId

mutex_id

)

Parameters

[in]

mutex_id

mutex ID obtained by osMutexCreate.

Returns

status code that indicates the execution status of the function.

Release a Mutex that was obtained with osMutexWait. Other threads that currently wait for the same mutex will be now put into the state READY.

Status and Error Codes

• osOK: the mutex has been correctly released.
• osErrorResource: the mutex was not obtained before.
• osErrorParameter: the parameter mutex_id is incorrect.
• osErrorISR: osMutexRelease cannot be called from interrupt service routines.

Note

Cannot be called from Interrupt Service Routines.

Example

#include "cmsis_os.h"
  
osMutexDef (MutexIsr);                                     // Mutex name definition 
osMutexId mutex_id;                                        // Mutex id populated by the function CreateMutex()
osMutexId CreateMutex (void);                              // function prototype that creates the Mutex
 
void ReleaseMutex (osMutexId mutex_id)  {
osStatus status;
  
  if (mutex_id != NULL)  {
    status = osMutexRelease(mutex_id);
    if (status != osOK)  {
      // handle failure code
    }
  }
}

osStatus osMutexWait	(	osMutexId	mutex_id,
		uint32_t	millisec
	)

Parameters

[in]	mutex_id	mutex ID obtained by osMutexCreate.
[in]	millisec	Timout Value or 0 in case of no time-out.

Returns

status code that indicates the execution status of the function.

Wait until a Mutex becomes available. If no other thread has obtained the Mutex, the function instantly returns and blocks the mutex object.

The argument millisec specifies how long the system waits for a mutex. While the system waits the thread that is calling this function is put into the state WAITING. The millisec timeout can have the following values:

• when millisec is 0, the function returns instantly.
• when millisec is set to osWaitForever the function will wait for an infinite time until the mutex becomes available.
• all other values specify a time in millisecond for a timeout.

Status and Error Codes

• osOK: the mutex has been obtain.
• osErrorTimeoutResource: the mutex could not be obtained in the given time.
• osErrorResource: the mutex could not be obtained when no timeout was specified.
• osErrorParameter: the parameter mutex_id is incorrect.
• osErrorISR: osMutexWait cannot be called from interrupt service routines.

Note

Cannot be called from Interrupt Service Routines.

Example

#include "cmsis_os.h"
  
osMutexDef (MutexIsr);
  
void WaitMutex (void)  {
osMutexId mutex_id;   
osStatus status;
 
  mutex_id = osMutexCreate  (osMutex (MutexIsr));
  if (mutex_id != NULL)  {
    status  = osMutexWait    (mutex_id, 0);
    if (status != osOK)  {
      // handle failure code
    }
  }
}