How do I implement a UART readCallback function ?

Hi Roy,

Your code is correct, the next step depends on what you want your application to do.
I would recommend that you have a separate task in your application in order to process the data that you're reading. In that case you would post a semaphore from the UART callback function to unblock that task.

So in the callback you could:
1. Move the data into a different buffer accessible by the uart data processing task.
2. Post a semaphore signaling that data has been received

Best,
Alexander

4401.com.cHi Alexander,  

I guess I am not sure how Uart_read() operates when you use it in the callback mode.  The information I gleaned from the forum said that each time I call UART_read(), it will then execute the callback function.  In the callback function I need to place another call to UART_read(), and then read the returned number of bytes from the buffer.   I believe I have done this in readCallBack().  However, I am getting zero bytes read, even though on my logic analyzer I can see a 5 byte packet being sent from my test equipment.

Please see my attached file com.c

Roy

Hi Roy,

UART_read() will have a callback function that is executed when all bytes have been received from the UART source. It is not recommended to call UART_read from its own callback as this can potentially lead to stack overflow issues. We recommend posting a semaphore from the callback function and to handle subsequent reads from within your task.

void readCallback(UART_Handle handle, void *buffer, size_t num)
{
    Semaphore_post(readSem);
}

Void testFxn1(UArg a0, UArg a1)
{
    //UART Initialization here..

    for(i = 1; i < 10; i++) {
        readSize = 6;
        UART_read(handle, input , readSize);
        Semaphore_pend(readSem, BIOS_WAIT_FOREVER);
    }
}

From the drivers documentation:

Source:
software-dl.ti.com/.../_u_a_r_t_8h.html

Best,

Alexander

Hi Alexander,

I took your advice and implemented my UART_read() in a task, and a semaphore post from the callback.

void readCallBack(UART_Handle handle, void *buffer, size_t num )

{

/*

* This callback is executed after the specified number of bytes have been

* read from UART_read(). Note that this number is always 1 byte.

*/

Semaphore_post( uart_read_sem );

} // end of readCallBack() ***************************************************

void uart_read_fxn( void )

{

extern void increment_index( BYTE *index_ptr );

extern BYTE detect_packet( void );

extern BYTE bytes_available( void );

BYTE buffer[LOB];

int bytes_read;

BYTE i;

while( 1 )

{

bytes_read = UART_read( uart_handle, &buffer, 1 );

Semaphore_pend( uart_read_sem, BIOS_WAIT_FOREVER );

if(bytes_read > 0)

{

for(i=0; i<bytes_read; i++)

{

// save the data

uart_read_buffer[ write_index_URB ] = buffer[i];

write_index_URB++;

if( write_index_URB >= LOURB)

{

write_index_URB = 0;

}

}

}

if( read_index_URB != write_index_URB )

{

// something was read from the UART

// detect_packet();

}

} // end of while( 1 )

} // end of uart_read_fxn() **************************************************

If I set a breakpoint after Semaphore_pend(), I get hits on it when a 5 byte packet is sent to the uart.  However, the number of bytes read is always zero.  It knows that there is activity, but it won't give me the received data.

Can you see anything wrong with my implementation ?

Thank you for your help.

Roy

7485.com.c

HI Alexander,

Following your explanation, reception of packets is now working a lot better. Thank you very much for the assistance.

However, I am seeing about 2 out of 5 packets corrupted. Typically, the first 4 bytes are OK, and then the last byte is corrupted.

Do you have any ideas on how to troubleshoot this issue ?

Roy

Hi Roy,

That's strange, are you seeing this behavior if you use blocking mode as well?

Best,
Alexander

Hi Alexander,

The blocking mode works flawlessly.  When my test system launches I know that the first packet it sends to me contains 5 bytes.  For 20 launches of my test system, I got the 5 byte packet correctly every time. 

BYTE buffer[LOB];

int read_size = 5;

BYTE i;

 

while( 1 )

{

       UART_read( uart_handle, &buffer, read_size );

 

       // Semaphore_pend( uart_read_sem, BIOS_WAIT_FOREVER );

 

       for(i=0; i<read_size; i++)

       {

              // save the data

              uart_read_buffer[ write_index_URB ] = buffer[i];

              write_index_URB++;

              if( write_index_URB >= LOURB)

              {

                     write_index_URB = 0;

              }

       }

}

Thanks

Roy

Hi again Roy,

Apologies for the late reply. I'm still unable to reproduce your issue. Could you run the attached modified uartecho example and let me know if you're able to see corruption on your end? Note this project is for the 5529 launchpad and may require a change in the board file to align the UART pins to your specific board.

7875.uartecho.zip

Best,

Alexander