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PIC32 UART Driver Accessing From Queue Task

Posted by Scott Olson on November 5, 2012
Hello, I have created a project that was started from the PIC32 UART driver demo. I started out with a simple task that ran periodically and successfully wrote to the UART. I then modified the task so that it uses a queue to get a message and then access the UART. Now it gets thrown into the general exception handler any time it calls any of the functions in the UART driver.

I have tried re-initializing the UART after the queue receive. I am really struggling to understand why I can talk to the UART before the block and wait for queue, but not after. Can anyone please shed some light on what may be going wrong here?

Thank you in advance, I am about 18 hours in to debugging this with no progress :)

Processor: PIC32MX795F512L
Dev Board: PIC32 USB Starter Kit II
Compiler: C32
FreeRTOS version: 7.2

Here is the code:

#define YIELDING_TIME_UART ( 10 / portTICK_RATE_MS ) //5ms
#define SIZE_OF_BUFFER_IN 63
// ----------------------------------------------
// ----------------------------------------------
static portTASK_FUNCTION_PROTO( vSerialTestTask, pvParameters );

// ----------------------------------------------
// ----------------------------------------------
xTaskHandle* handle;
static char buffer_in[SIZE_OF_BUFFER_IN];
static char buffer_out[SIZE_OF_BUFFER_OUT];
static char second_buffer_out[SIZE_OF_BUFFER_OUT];
static int position = 0;
static int cr_received;

xQueueHandle xQueueHandleGSMSend2;
LogMessage* lReceivedData2;

// ----------------------------------------------
// ----------------------------------------------
void StartSerialTestTask( unsigned portBASE_TYPE priority ){

cr_received = FALSE;
//UARTInit( 2, 9600 );
UARTInit( 1, 115200 );

xQueueHandleGSMSend2 = xQueueCreate(5, sizeof(LogMessage));
//creates task
xTaskCreate( vSerialTestTask, ( signed char * ) "Serial test", UART_STACK_SIZE, NULL, priority, ( xTaskHandle * ) handle );

static portTASK_FUNCTION( vSerialTestTask, pvParameters ){
portBASE_TYPE xStatus;
int retVal;
int i;

//cleans buffers
for(i=0; i buffer_out = '\0';
second_buffer_out = '\0';


//clears input buffer
for( i=0; i buffer_in = '\0';


xStatus = xQueueReceive(xQueueHandleGSMSend2, &lReceivedData2, portMAX_DELAY);

if(xStatus == pdPASS)



RE: PIC32 UART Driver Accessing From Queue Task

Posted by Dave on November 5, 2012
You create a queue that holds five messages of sizeof(LogMessage) bytes. I don't know how many bytes that is, but will assume it is more than 4 -

xQueueHandleGSMSend2 = xQueueCreate(5, sizeof(LogMessage));

You create a variable that is a pointer to a LogMessage. A pointer on a PIC32 is 4 bytes -

LogMessage* lReceivedData2;

You then copy sizeof(LogMessage) bytes into the variable that is 4 bytes -

xStatus = xQueueReceive(xQueueHandleGSMSend2, &lReceivedData2, portMAX_DELAY);

If sizeof(LogMessage) bytes is more than four then more than four bytes will be copied into the pointer, and you will corrupt your stack. Even if sizeof(LogMessage) is only 4 bytes, you will not end up with a pointer to a log message. I suspect you want to do something like this -

Create a variable that is a LogMessage (not a pointer to one) -

LogMessage lReceivedData2;

Copy a log message from the queue into the variable that is of type LogMessage -

xStatus = xQueueReceive(xQueueHandleGSMSend2, &lReceivedData2, portMAX_DELAY);

Not related to your problem, but this code -

    //cleans buffers
for(i=0; i buffer_out = '\0';
second_buffer_out = '\0';

does not appear to do anything except repeatedly set the same two variables to \0.

same comment for this code -

      //clears input buffer
for( i=0; i buffer_in = '\0';

RE: PIC32 UART Driver Accessing From Queue Task

Posted by Scott Olson on November 5, 2012
Thanks for the help, this fixed it! I have been writing only c# for the last 10 years, I guess my pointer and memory management skills are pretty rusty.... Thanks again for the help!

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