Create task with multiple queues in FreeRTOS?

Question

I'm having trouble sending multiple queues to a task in FreeRTOS.

I've tried creating a struct to hold them like this:

typedef struct
{
    xQueueHandle buttonQueue;
    xQueueHandle OLEDQueue;
} xQueues;

and then sending it to the task like this:

void vStartADCtasks( xQueueHandle xButtonQueuex, QueueHandle xOLEDQueue )
{
    xQueues xADCQueues = { xOLEDQueue, xButtonQueue };
    xTaskCreate( vGetAltitude, "Get Altitude", 240, (void *) &xADCQueues, 2, NULL );
}

and accessing it like this in the task:

static void vGetAltitude(void *pvParameters) {
    xQueues *xADCQueues = ( xQueues * ) pvParameters;
    xQueueHandle xOLEDQueue = xADCQueues->OLEDQueue;
    xQueueHandle xButtonQueue = xADCQueues->buttonQueue;

but that doesn't work. Any tips? I guess my more general question is how to pass around a queue between multiple .c files. ie. create it and one file, but be able to use it in a task in another file?

score 6 · Accepted Answer · answered Jul 17 '13 at 05:41

You've got 3 bugs. First is that you've swapped the order of the queues when you try initializing xADCQueues. Second, you should pass xADCQueues as the 4th argument to xTaskCreate. Third, your xADCQueues struct is created on the stack, which means that after vStartADCtasks returns, that struct is destroyed and overwritten.

Replace your vStartADCtasks with this

xQueues xADCQueues;
void vStartADCtasks( xQueueHandle xOLEDQueue, xQueueHandle xButtonQueue )
{
    xADCQueues.buttonQueue = xButtonQueue;
    xADCQueues.OLEDQueue = xOLEDQueue;
    xTaskCreate( vGetAltitude, "Get Altitude", 240, (void *) &xADCQueues, 2, NULL );
}

or don't bother creating xADCQueues at all, but just make xButtonQueue and xOLEDQueue global variables. I don't see anything wrong with doing that for embedded systems... I know they teach you in school to avoid global variables, but in this case, it is a good idea to make the variables global and static since they are shared by tasks.

Man I made some silly mistakes there. Thankyou! In terms of the global variable situation with queues, with multiple .c/.h files would that still be OK (using extern in the header files)? — routeburn, Jul 17 '13 at 05:48
if those queues should not be shared then allocate a queue per task, if they are to be shared then some synchronization may be need. hope you're not writing an airplane firmware anytime soon :) — iabdalkader, Jul 17 '13 at 05:52
Putting the queue declarations in a header file with extern is a fine way of doing it. — Mark Lakata, Jul 17 '13 at 14:06

Create task with multiple queues in FreeRTOS?

1 Answers1