Appendix A: Mutex callbacks

The mutexes are designed such that a call to ZPS_u8GrabMutexLock() must be followed by a call to ZPS_u8ReleaseMutexLock(). In addition, the call must not be followed by another call to ZPS_u8GrabMutexLock(), which means the mutexes are binary rather than counting. This can cause problems if the ZCL takes a mutex via the callback function and then the application wants to lock the mutex to access the shared device structures. Some ZCL clusters also invoke the callback function with E_ZCL_CBET_LOCK_MUTEX multiple times. The counting mutex code below should be used in the application code. When the application wants to access the shared structure, it should call the vLockZCLMutex() function (shown in the code extract below), rather than ZPS_u8GrabMutexLock(), so that it also participates in the counting mutex rather than directly taking the binary ZPS mutex-protection. Similarly, the shared structure should be released using vUnlockZCLMutex().

The code below uses a single resource for all endpoints and the general callback function. It defines a file scope counter that is the mutex count related to the resource.

At the top of the application source file, create the count and lock/unlock mutex function prototypes (these prototypes may be placed in a header file, if desired):

uint32  u32ZCLMutexCount  =  0;
void  vLockZCLMutex(void);
void  vUnlockZCLMutex(void);
                

In both cbZCL_GeneralCallback() and cbZCL_EndpointCallback(), make the calls:

switch(psEvent->eEventType)
 {
 case  E_ZCL_CBET_LOCK_MUTEX:
              vLockZCLMutex();
            break;
      case  E_ZCL_CBET_UNLOCK_MUTEX:
        vUnlockZCLMutex();
            break;

Define the lock/unlock mutex functions and call them from the application when accessing any ZCL shared structure:

void  vLockZCLMutex(void)
{
        if  (u32ZCLMutexCount  ==  0)
        {
                ZPS_u8GrabMutexLock(mutexZCL,0);
        }
        u32ZCLMutexCount++;
}
void  vUnlockZCLMutex(void)
{
        u32ZCLMutexCount--;
        if  (u32ZCLMutexCount  ==  0)
        {
                ZPS_u8ReleaseMutexLock(mutexZCL,0);
        }
}