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ISR and queue handling

Posted by Casper Hedegaard on January 14, 2013

Controller: Atmel UC3A0512
Enviroment: ARV32 Studio

I have a USART interrupt which is like this:

__attribute__((__interrupt__)) static void usart_int_handler( void )
static int status, temp;
static uint8_t data;

static portBASE_TYPE xHigherPriorityTaskWoken;
xHigherPriorityTaskWoken = pdFALSE;

// Read USART buffer
status = usart_read_char( USART_CHANNEL, &temp );

if( USART_RX_ERROR == status)
// Resetting the USART
usart_reset( USART_CHANNEL );

// Enable the USART as RS485
else if( USART_SUCCESS == status )
data = (uint8_t)temp;

// Because FreeRTOS is not supposed to run with nested interrupts, put all OS calls in a critical section
xQueueSendToBackFromISR( xRXQueue, &data, &xHigherPriorityTaskWoken );

if( xHigherPriorityTaskWoken == pdTRUE )
// Force unblocked (higher priority) tasks to run

I'm running in multidrop mode and I have 2 slave modules connected to this RS485 bus.

My problem is that when my task, which is looking at this xRXQueue, is seeing data in the queue and starts to read the queue, the system breaks down and restarts do to my watchdog. The task starts like this:

if( pdPASS == xQueueReceive(xRXQueue, rx_buf, portMAX_DELAY) )
// code here

How can I, in a more secure way, handle this queue and interrupt handling so it will not stall the controller?

Best regards

RE: ISR and queue handling

Posted by Richard on January 14, 2013
There does not look to be anything fundamentally wrong with your implementation. Are you using the ARV32 port that is distributed by Atmel, which is the version for the latest AV32 chips?


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