FreeRTOS: Queue did not work as expected - queue

Question

I am new to FreeRTOS. I have written an example using queue to transfer data between tasks. Nevertheless, the results displayed are wrong. May anyone help me to get over this problem?
Thanks!
Variables to be displayed:
unsigned int temperatureRaw = 25;
unsigned int flowRateRaw = 30;
unsigned int carbonLevelRaw = 250;
unsigned int salinityLevelRaw = 75;
Struct holding pointers to above variables:
struct RawData {
unsigned int *temperatureRaw;
unsigned int *flowRateRaw;
unsigned int *carbonLevelRaw;
unsigned int *salinityLevelRaw;
};
typedef struct RawData RawData;
Tasks' prototype
static void vOLEDTask( void *pvParameters );
static void vTask1( void *pvParameters );
static void prvSetupHardware( void );
Queue handles:
QueueHandle_t xOLEDQueue, xRawQueue;
Main:
int main( void )
{
prvSetupHardware();
/* Create queues */
xOLEDQueue = xQueueCreate( mainOLED_QUEUE_SIZE, sizeof( xOLEDMessage * ) );
xRawQueue = xQueueCreate( 3, sizeof( RawData * ) );
/* Check if queues are successfully created */
if( ( xOLEDQueue != 0 ) && ( xRawQueue != 0 ) ) {
// Declare variables
RawData xRawData = { &temperatureRaw, &flowRateRaw, &carbonLevelRaw, &salinityLevelRaw };
RawData *pxRawData = &xRawData;
/* Start the tasks defined within this file/specific to this demo. */
xTaskCreate( vOLEDTask, "OLED", mainOLED_TASK_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL );
xTaskCreate( vTask1, "Task1", 1000, ( void * )pxRawData, 1, NULL );
/* Start the scheduler. */
vTaskStartScheduler();
}
return 0;
}
Tasks' definition:
void prvSetupHardware( void )
{
/* If running on Rev A2 silicon, turn the LDO voltage up to 2.75V. This is
a workaround to allow the PLL to operate reliably. */
if( DEVICE_IS_REVA2 )
{
SysCtlLDOSet( SYSCTL_LDO_2_75V );
}
/* Set the clocking to run from the PLL at 50 MHz */
SysCtlClockSet( SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_8MHZ );
}
void vOLEDTask( void *pvParameters )
{
RawData *pxRawData = NULL;
unsigned long ulMaxY;
static char cMessage[ mainMAX_MSG_LEN ];
extern volatile unsigned long ulMaxJitter;
const unsigned char *pucImage;
/* Functions to access the OLED. The one used depends on the dev kit
being used. */
void ( *vOLEDInit )( unsigned long ) = NULL;
void ( *vOLEDStringDraw )( const char *, unsigned long, unsigned long, unsigned char ) = NULL;
void ( *vOLEDImageDraw )( const unsigned char *, unsigned long, unsigned long, unsigned long, unsigned long ) = NULL;
void ( *vOLEDClear )( void ) = NULL;
/* Map the OLED access functions to the driver functions that are appropriate
for the evaluation kit being used. */
switch( HWREG( SYSCTL_DID1 ) & SYSCTL_DID1_PRTNO_MASK )
{
case SYSCTL_DID1_PRTNO_6965 :
case SYSCTL_DID1_PRTNO_2965 : vOLEDInit = OSRAM128x64x4Init;
vOLEDStringDraw = OSRAM128x64x4StringDraw;
vOLEDImageDraw = OSRAM128x64x4ImageDraw;
vOLEDClear = OSRAM128x64x4Clear;
ulMaxY = mainMAX_ROWS_64;
pucImage = pucBasicBitmap;
break;
case SYSCTL_DID1_PRTNO_1968 :
case SYSCTL_DID1_PRTNO_8962 : vOLEDInit = RIT128x96x4Init;
vOLEDStringDraw = RIT128x96x4StringDraw;
vOLEDImageDraw = RIT128x96x4ImageDraw;
vOLEDClear = RIT128x96x4Clear;
ulMaxY = mainMAX_ROWS_96;
pucImage = pucBasicBitmap;
break;
default : vOLEDInit = vFormike128x128x16Init;
vOLEDStringDraw = vFormike128x128x16StringDraw;
vOLEDImageDraw = vFormike128x128x16ImageDraw;
vOLEDClear = vFormike128x128x16Clear;
ulMaxY = mainMAX_ROWS_128;
pucImage = pucGrLibBitmap;
break;
}
/* Initialise the OLED and display a startup message. */
vOLEDInit( ulSSI_FREQUENCY );
for( ;; )
{
xQueueReceive( xRawQueue, ( void * )&pxRawData, portMAX_DELAY );
/* Display the message. */
sprintf( cMessage, "%s %u C", "Temperature", *(pxRawData->temperatureRaw) );
vOLEDStringDraw( cMessage, 0, 10, mainFULL_SCALE );
sprintf( cMessage, "%s %u LPS", "Flow Rate", *(pxRawData->flowRateRaw) );
vOLEDStringDraw( cMessage, 0, 20, mainFULL_SCALE );
sprintf( cMessage, "%s %u ppm", "Carbon Level", *(pxRawData->carbonLevelRaw) );
vOLEDStringDraw( cMessage, 0, 30, mainFULL_SCALE );
sprintf( cMessage, "%s %u ppt", "Salinity Level", *(pxRawData->salinityLevelRaw) );
vOLEDStringDraw( cMessage, 0, 40, mainFULL_SCALE );
}
}
/*-----------------------------------------------------------*/
static void vTask1( void *pvParameters )
{
RawData *pxRawData = ( RawData * )pvParameters;
for( ;; ) {
xQueueSend( xRawQueue, ( void * )&pxRawData, portMAX_DELAY );
vTaskDelay( 1000/portTICK_RATE_MS );
}
}

Answer 1

I have not studied all the code, but the first problem I see is that you are passing pxRawData as a parameter to a task, pxRawData is a pointer to xRawData, but xRawData has a very narrow block scope, and the stack it is declared on is different to the stack used by the task, so the variable being pointed to will not exist when the task starts running - or if it does exist it is by luck and there is a risk it will get overwritten (depending on the FreeRTOS port being used).
Also, consider that xRawQueue is created to hold pointers to RawData, but I think your call to xQueueSend in vTask1 is passing the address of a pointer, so it is queuing a pointer to a pointer to RawData, not a pointer to RawData. Although that probably doesn't matter as its being received into a pointer to a pointer too, and then accessed as such.