mqttsn with openthread and freertos

Question

I am trying to hook openthread with freeRTOS. 
 Short story: the current state of my implementation is that I get a hardfault after succesfully calling mqttsn_client_search_gateway, but before receiving any data on the other end on the mqtt-sn gateway. The stack at this point starts in 
 > strace warning: Couldn't determine the static tracepoint marker to probe Static tracepoint 16 at 0x7d8a: file nRF5_SDK\external\freertos\portable\GCC
rf52\port.c, line 104. 
 
 Long story: 
 From freeRTOS, I am mostly interested in tasks and message queues. 
 My skeleton implementation has 2 tasks: 
 1. the openthread processing thread: 
 
 static SemaphoreHandle_t threadMutex = nullptr ; 
 
 static void thread_stack_task ( void* ) 
 { 
 while ( 1 ) 
 { 
 xSemaphoreTake ( threadMutex , portMAX_DELAY ); 
 thread_process (); 
 xSemaphoreGive ( threadMutex ); 
 UNUSED_RETURN_VALUE ( ulTaskNotifyTake ( pdTRUE , portMAX_DELAY )); 
 } 
 } 
 
 and starting it like in one of the examples:

threadMutex = xSemaphoreCreateMutex (); 
 
 // Start thread stack execution. 
 if ( pdPASS != xTaskCreate ( thread_stack_task , "THR" , THREAD_STACK_TASK_STACK_SIZE , NULL , THREAD_STACK_TASK_PRIORITY , &thread_stack_task_handle)) 
 { 
 APP_ERROR_HANDLER ( NRF_ERROR_NO_MEM ); 
 } 
 
 The other task is a state machine to handle different states in the connection process: 
 - initializing the thread structures 
 - joining a thread network: role changes to CHILD or ROUTER 
 - searching for a mqtt-sn gateway 
 - connecting the mqtt client, etc. 
 Here's how I start the state machine task (ConnectionStateMachine is a singleton for some other reasons later on) : 
 
 csm = ConnectionStateMachine :: GetInstance (); 
 csm -> SetThreadMutex ( threadMutex ); 
 if ( pdPASS != xTaskCreate ( 
 []( void* stateMachine )-> void 
 { 
 (( ConnectionStateMachine *) stateMachine )-> StateMachine (); 
 }, 
 "CSM" , THREAD_STACK_TASK_STACK_SIZE , csm , THREAD_STACK_TASK_PRIORITY , &thread_stack_task_handle)) 
 { 
 APP_ERROR_HANDLER ( NRF_ERROR_NO_MEM ); 
 } 
 
 and the StateMachine method: 
 
 void ConnectionStateMachine :: StateMachine () 
 { 
 while ( true ) 
 { 
 Event event ; 
 if ( pdTRUE == xQueueReceive ( messasgeQueue , & event , portMAX_DELAY )) 
 { 
 xSemaphoreTake ( m_threadMutex , portMAX_DELAY ); 
 switch ( state ) 
 { 
 case StateUnitialized : 
 {

if ( event == EventInitialized ) 
 { 
 //auto transition to an initialized state 
 ThreadInstanceInit (); 
 m_client . Init (); 
 
 state = StateInitialized ; 
 } 
 break ; 
 }

where state is the state, and event is the transition. 
 To transition from a state, one needs to call: 
 
 bool ConnectionStateMachine :: Transition ( Event desiredTransition ) 
 { 
 bool retValue ; 
 //return false if the queue is full (in the middle of processing a state transition) 
 retValue = ( xQueueSend ( messasgeQueue , & desiredTransition , ( TickType_t ) 0 ) == pdTRUE ? true : false ); 
 return retValue ; 
 } 
 
 The idea is that the callback in openthread and mqtt are on the context of the Thread task, and I can quickly wake up my StateMachine by adding a message to the queue: 
 
 static void state_changed_callback ( uint32_t flags , void * p_context ) 
 { 
 if ( flags & OT_CHANGED_THREAD_ROLE ) 
 { 
 otDeviceRole role = otThreadGetDeviceRole (( otInstance *) p_context ); 
 if ( role == OT_DEVICE_ROLE_CHILD || role == OT_DEVICE_ROLE_ROUTER ) 
 { 
 ConnectionStateMachine :: GetInstance ()-> Transition ( ConnectionStateMachine :: EventConnected ); 
 } 
 } 
 } 
 
 I can reach this part, and even transtion to the next state, where I call mqttsn_client_init and then call mqttsn_client_search_gateway successfully, with a return code NRF_SUCCESS. After this, I do not see any data transmitted to the gateway, not reaching the event handler callback set in the init function, and quickly (a few seconds) crashing in a hardfault originating from nRF5_SDK\external\freertos\portable\GCC
rf52\port.c:104 in 
 
 void xPortPendSVHandler ( void ) 
 
 At this point I have no ideas what to try to debug anymore. Any help is highly appreciated. 
 
 Thanks, 
 Edgar

EdgarGrimberg · Answer

OK, I think I got it. I was single stepping through the mqttsn code, when stack overflow handler kicked. Really lucky here! 
 Here's what the current TCB was showing: 
 
 So it was the timer task that was running low on stack. The solution, of course, was to increase the task size for the timer task. 
 In FreeRTOSConfig.h, I bumped the timer task stack depth to 160: 
 
 #define configTIMER_TASK_STACK_DEPTH ( 160 ) 
 
 And it all went fine from there. 
 Thanks for pointing me into the right direction, really appreciate the support! 
 Regards, 
 Edgar

mqttsn with openthread and freertos

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