I'm trying to set up a task that will regularly check the rx message queue on uart, and I have the ISR working properly, but whenever I try to read the contents of the rx message queue I receive the character, but the mcu crashes immediately afterwards. Also, if no character is input before xQueuePeek times out (500 ticks in this case) it will also crash. If I remove the code to check the rx queue, it works fine and happily writes to the uart every 100 ticks as expected.

I just ordered the freertos book (hopefully I'll get it today), but if there something that I'm doing in this task code that I obviously shouldn't be? (All I'm trying to do it send the char back out to the UART just to see if it works or not.)

static portTASK_FUNCTION(vUART1Task, pvParameters __attribute__((unused)))
{
static xQueueHandle rxQueue = NULL;
uart1GetRxQueue (&rxQueue);
signed portCHAR rxChar;

for (;;)
{
/* Check if anything is available in the rx queue */
if (rxQueue)
{
if (xQueuePeek(rxQueue, &rxChar, (portTickType)500))
{
/* Print the result on the uart port */
char *feedback;
sprintf(feedback, "Received: %c\r\n", rxChar);
uart1PutString(feedback, 10);
}
}

// Transmit current tick on UART1
char *output;
sprintf(output, "Ticks: %d\r\n", xTaskGetTickCount());
uart1PutString(output, 10);
vTaskDelay(100);
}
}

It seems that it isn't actually the queues, but the sprintf that's causing the problems. The following code seems to work as expected:

/* Check if anything is available in the rx queue */
if (rxQueue)
{
if (xQueueReceive(rxQueue, &rxChar, (portTickType)500)) // portMAX_DELAY))
{
/* Print the result on the uart port */
uart1PutString("Received: ", portMAX_DELAY);
uart1PutChar(rxChar, portMAX_DELAY);
uart1PutString("\r\n", portMAX_DELAY);
}
}

char *feedback;
With this line you allocate a character pointer, but no memory to hold the string to which it points. The pointer is uninitialized.

sprintf(feedback, "Received: %c\r\n", rxChar);
With this line you are writing a dozen characters into an address pointed to by an uninitialized pointer, so it will more than likely crash.

Ooops ... so busy looking at the queues that I don't pay attention to what's right in front of my eyes :)

/* Print the result on the uart port */
char feedback[80];
sprintf(feedback, "Received: %c\r\n", rxChar);
uart1PutString(feedback, 10);

that should be better, but make sure you have enough stack space to hold the 80 character array.