Problem with Array of Queues in FreeRTOS

Question

I am building a FreeRTOS application. I created a module which registers a freeRTOS queue handle from another module and when an interrupt in this module module occurs, it sends a message to all the registered queues. But it seems I am able to send the message from the queue but not able to receive it at the other module.

Here is my code.

remote module:-

  CanRxMsg RxMessage;
  can_rx0_queue = xQueueCreate( 10, sizeof(CanRxMsg) ); // can_rx0_queue is globally defined 
  // Register my queue with can module
  if (registerRxQueueWithCAN(can_rx0_queue) == -1)
  {
    TurnLedRed();
  }  

  while(1)
  {
        if(can_rx0_queue){
      while( xQueueReceive( can_rx0_queue, ( void * ) &RxMessage, portMAX_DELAY))
      {
}
.....

Here is the registration module

#define MAX_NUMBER_OF_RX_QUEUES 2

//xQueueHandle rxQueueStore[MAX_NUMBER_OF_RX_QUEUES];

typedef struct QUEUE_REGISTRY_ITEM
{
//  signed char *pcQueueName;
  xQueueHandle xHandle;
} xQueueRegistryItem;

xQueueRegistryItem rxQueueStore[MAX_NUMBER_OF_RX_QUEUES];

int numberOfQueuesRegistered;

#define cError -1

#define cSuccess 0

void processInterrupt()
{
 for(int i=0; i < numberOfQueuesRegistered; i++)
  {
    if(xQueueSendFromISR(rxQueueStore[i].xHandle,(void *) &RxMessage,&tmp) != pdTRUE)
        TurnLedRed();
    if(tmp)resched_needed = pdTRUE;
  }

  portEND_SWITCHING_ISR(resched_needed);
}

int registerRxQueueWithCAN(xQueueHandle myQueue)
{
  if(numberOfQueuesRegistered == MAX_NUMBER_OF_RX_QUEUES)
  {
    // Over Flow of registerations
    TurnLedRed();
    return cError; 
  }else 
  {
    rxQueueStore[numberOfQueuesRegistered].xHandle = myQueue;
    numberOfQueuesRegistered++;
  }
  return cSuccess;
}

Few points:-

1. xQuehandle is typdefed to "void *"
2. The code works if remove the registration thing and just do with directly pointer of queue in xQueueSendFromISR if I take the pointer by extern.

Any advice or information required?

Answer 1

At first glance I cannot see anything obviously wrong. The problem might be outside of the code you have shown, like how is can_rx0_queue declared, how is the interrupt entered, which port are you using, etc.

There is a FreeRTOS support forum, linked to from the FreeRTOS home page http://www.FreeRTOS.org

Regards.

Answer 2

I think Richard is right. The problem could be issues that are not within your code that you have posted here.

Are you calling any form of suspension on the receiving Task that is waiting on the Queue? When you invoke a vTaskSuspend() on a Task that is blocked waiting on a Queue, the Task that is suspended will be moved to the pxSuspendedTaskList and it will "forget" that it is waiting on an Event Queue because the pvContainer of xEventListItem in that Task will be set to NULL.

You might want to check if your receiving Task is ever suspended while waiting on a Queue. Hope that helped. Cheers!

Answer 3

Your shared memory should at least be declared volatile:

volatile xQueueRegistryItem rxQueueStore[MAX_NUMBER_OF_RX_QUEUES] ;
volatile int numberOfQueuesRegistered ;

otherwise the compiler may optimise out read or writes to these because it has no concept of different threads of execution (between the ISR and the main thread).

Also I recall that some PIC C runtime start-up options do not apply zero-initialisation of static data in order to minimise start-up time, if you are using such a start-up, you should explicitly initialise numberOfQueuesRegistered. I would suggest that to do so would be a good idea in any case.

It is not clear from your code that RxMessage in the ISR is not the same as RxMessage in the 'remote module'; they should not be shared, since that would allow the ISR to potentially modify the data while the receiving thread was processing it. If they could be shared, there would ne no reason to have a queue in the first place, since shared memory and a semaphore would suffice.

As a side-note, there is never any need to cast a pointer to void*, and you should generally avoid doing so, since it will prevent the compiler from issuing an error if you were to pass something other than a pointer. The whole point of a void* is rather that it can accept any pointer type.