UART Interrupt problem

[ikrajinovic]

Hi,

I have problem when recieving UART data using Interrupt. I use EasyPIC Fusion V7 and PIC32MX795F512L.

Everything works well when I sending 8 or less caraters to board. When I try to send more then 8 ISR doesn't worke anymore.

I attached all project files in zip.

Does anyone have some suggestion how to solve this problem.

Thank you.

BR,
Ivo

[hexreader]

The idea of using interrupts for UART receive is that your interrupt routine puts all received characters into a buffer, updates the buffer pointer(s) and gets out of the interrupt routine as fast as possible.

Your "main" loop should then handle the receive buffer at leisure, in the safe knowledge that interrupts will handle receive data as fast as it is sent.

You are spending far too much time processing each interrupt, so that incoming serial data is no longer being processed. There is only a 4 byte hardware buffer (IIRC) so there is limited hardware buffering.

As a terrible cludge, you could change UART5_Write_Text("---UART while: "); to UART5_Write_Text(":");
This may allow a few more bytes to be sent consecutively before disaster happens, but this would be a bodge, not a solution.

In summary: Use receive interrupts to fill a buffer of sufficient size for your application and do processing within main loop. Avoid intensive or slow processing within your interrupt routine.

[ikrajinovic]

Thank you.

Your suggestion solved my problem. I short ISR and everything works OK.

This is how it looks now:

Code: Select all

void UART5interrupt() iv IVT_UART_5 ilevel 6 ics ICS_AUTO {
  while(UART5_Data_Ready())
  {
   uart_rd = UART5_Read();        // read the received data
   txt[dataCounter] = uart_rd;
   dataCounter++;
  }

    if (dataCounter == 128)
    {
      dataCounter = 0;
    }

  dataFlag = 1;

  U5RXIF_bit = 0;
}

[ikrajinovic]

I have one more problem about reading UART data.
Everything works extremely well when i declare

Code: Select all

volatile char txt[BUFLEN + 1];

where BUFLEN is less than 255. But when I try to increase array length I have a program that is not working after first message arrived that is longer than 255 bytes. I declare constant for array length.

Code: Select all

const unsigned int BUFLEN = 256;

This is my ISR:

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void UART5interrupt() iv IVT_UART_5 ilevel 6 ics ICS_AUTO {
  while(UART5_Data_Ready() == 1)
  {
   uart_rd = UART5_Read();        // read the received data
   if(dataCounter < BUFLEN)
   {
    txt[dataCounter] = uart_rd;
    dataCounter++;
   }
  }
  dataFlag = 1;
  U5RXIF_bit = 0;
}

I main I have this:

Code: Select all

while(1)
  {
     if (dataFlag == 1 && UART5_Data_Ready() == 0){

       dataFlag = 0;
       txt[dataCounter] = '\0';
       
       if(dataCounter > 0)
       {
         UART5_Write_Text(txt);
         UART5_Write(13);
         UART5_Write(10);
       }
       else
       {
         UART5_Write_Text("Buffer is empty");
         UART5_Write(13);
         UART5_Write(10);
       }
       dataCounter = 0;
       memset( txt, 0, (BUFLEN+1));
     }
}

[hexreader]

Did you change declaration of dataCounter from unsigned short (0 to 255) to unsigned int (0 to 65535)?

[ikrajinovic]

Yes. Now it is

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volatile unsigned int dataCounter = 0;

[ikrajinovic]

The problem was in library function UARTx_Write_Text.

This function was unable to send string longer than 255 caracters.

I made custom function and now everything works great.

Code: Select all

void UART5_Write_String(const char* str) {
    int i = 0;
    for (i = 0 ; str[i]!='\0' ; i++) {
        UART5_Write(str[i]);
    }
}

[serge87]

I encountered the UARTx_Write_Text 255 charater limit in mikrobasic too.
In the help file it doesn't specify a limit to the amount of characters you can sent trough UARTx_Write_Text.
I had to make my own function as well in order to sent a larger buffer trough UART, actually checking for the null at the end of the string rather than using a loop variable.