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[PIC] UART code for flowcontrol enable

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rajalakshmiA

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Hi
I am using PI32MX795f512l .. I want to integrate flowcontrol in my uart communication .. As of now i am using only TX and RX pins for data transmit and receive ...
In Continous transmission ,in bluetooth module i am getting overwritten buffer...Pls Help me to come out of this.. I am new one to this.... How to enable flowcontrol in my uart code. Here i have attached my code below

Code C - [expand]
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#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_1
#define SYS_FREQ (80000000L)
#pragma config ICESEL = ICS_PGx1
 
void init_uart()
{
    UARTConfigure(UART_MODULE_ID, UART_ENABLE_PINS_TX_RX_ONLY);
    UARTSetFifoMode(UART_MODULE_ID, UART_INTERRUPT_ON_TX_NOT_FULL | UART_INTERRUPT_ON_RX_NOT_EMPTY);
    UARTSetLineControl(UART_MODULE_ID, UART_DATA_SIZE_8_BITS | UART_PARITY_NONE | UART_STOP_BITS_1);
    UARTSetDataRate(UART_MODULE_ID, GetPeripheralClock(), DESIRED_BAUDRATE);
    UARTEnable(UART_MODULE_ID, UART_ENABLE_FLAGS(UART_PERIPHERAL | UART_RX | UART_TX));
}
void Uart_Interrupt(){
INTEnable(INT_SOURCE_UART_RX(UART_MODULE_ID), INT_ENABLED);
    INTSetVectorPriority(INT_VECTOR_UART(UART_MODULE_ID), INT_PRIORITY_LEVEL_2);
    INTSetVectorSubPriority(INT_VECTOR_UART(UART_MODULE_ID), INT_SUB_PRIORITY_LEVEL_0);
 
    // Enable multi-vector interrupts
    INTConfigureSystem(INT_SYSTEM_CONFIG_MULT_VECTOR);
    INTEnableInterrupts();
}
main()
{
   init_uart();
   Uart_Interrupt();
   while(1){
    if(flag ==1){ // some code}
   }
   
}
void __ISR(_UART2_VECTOR,IPL2) IntUart2Handler(void)
{
    unsigned char Receivedchar;
    if(INTGetFlag(INT_SOURCE_UART_RX(UART_MODULE_ID)))
    {
        Receivedchar= UARTGetDataByte(UART_MODULE_ID);
        ReceivedByte[buf]=Receivedchar;
        buf++;
        count++;
        flag=1;
        INTClearFlag(INT_SOURCE_UART_RX(UART_MODULE_ID));
 
    }
        
   // We don't care about TX interrupt
    if ( INTGetFlag(INT_SOURCE_UART_TX(UART_MODULE_ID)) )
    {
        INTClearFlag(INT_SOURCE_UART_TX(UART_MODULE_ID));
    }
}
 
Last edited by a moderator:

Hi,

did you read documents about UART software flow control?

***
Check: (to avoid software flow control)
* if reducing / increasing the baud rate may solve your problem
* if the receiver software could be optimized to avoid buffer overflow. (latency times, buffer size)

Klaus
 

To start with, flowcontrol from a microcontroller is not really complex. There are two flow control models usually: hardware and software.

For hardware, the sender asserts RTS (request to send). The receiver responds with CTS (clear to send). In principle, you could use a pair of GPIO pins for RTS/CTS signals. I did not see the uC datasheet myself. But, in ideal scenario, the RTS should have peripheral input interrupt enabled on it. Here is a rough algoirthm:

=============================================
On RTS Assert (or Interrupt):
if (buffer full):
continue # The device holds the data in its buffer.
else
assert CTS
get a byte

On receive byte (or Interrupt):
if (buffer full):
de-assert CTS
=========================================

The software flow control uses a pair of control characters - XON/XOFF. Search around for software flow control in, say, Google.

I would start with datasheets. If the baudrate could be reduced, that'll be a very good place to start. The primary requirement in any case is: the sending device must support flow control - either software or hardware.
 

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