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Serial interrupt behaviour?

Michael Gustafsson

Hi everyone!

I'm a n00b to microcontroller programming so have patience with me :)

The mission is to handle some uart (rs232) communication, both rx and tx. My part is a small module going into a rest of the software already developed.

The issue is the following: When I use serial ISR it seems to not go into the "main while loop" (which is required).

(I've also tried to poll my self but reliability seems somewhat unstable, loosing a byte here and there)

I've tried the simplest demo/test programs and if I for instance use a printf in the while loop, it will not reach it as soon as ES = 1.

Is it just that any printf will not issue an interrupt and hence no output to my terminal? At the moment I can not test my module with the rest of the software so I'm a bit in the blind here, well could of course try to blink a led or something... but I reacon a answer from here is faster and more reliable :)

Thanks in advance

/Mike

Parents
  • 0 in reply to Christoph Franck

    Of course here it is:

    #include "at89c5131.h"
    #include "stdio.h"

    char uart_data

    void main (void)
{
    int i=0;

    uartInit();

    // Global interrupt
    EA = 1;

    // Serial interrupt
    // Comment out below and printf in while will work
    ES = 1;

    while(1)
    {
        printf("...");
    }
}

// The ISR function echos the received character
void serial_IT(void) interrupt 4
{
    if(RI==1)
    {
        RI=0;
        uart_data = SBUF; //Read received data
        SBUF = uart_data; //Send back same data on uart
    }
    else TI=0;
}

Reply
  • 0 in reply to Christoph Franck

    Of course here it is:

    #include "at89c5131.h"
    #include "stdio.h"

    char uart_data

    void main (void)
{
    int i=0;

    uartInit();

    // Global interrupt
    EA = 1;

    // Serial interrupt
    // Comment out below and printf in while will work
    ES = 1;

    while(1)
    {
        printf("...");
    }
}

// The ISR function echos the received character
void serial_IT(void) interrupt 4
{
    if(RI==1)
    {
        RI=0;
        uart_data = SBUF; //Read received data
        SBUF = uart_data; //Send back same data on uart
    }
    else TI=0;
}

Children
  • 0 in reply to Michael Gustafsson

    Of course here it is:

    uart_init() would also be of interest.

    Also, as I mentioned below, using printf() and using interrupt-driven operation on the UART at the same time is most likely a bad idea. You may need to find a different method to indicate that the program has entered the main loop (e.g. toggle a port pin or blink a LED - or use a breakpoint if your emulator/debugger supports it).

  • 0 in reply to Michael Gustafsson 

    void uartInit(void);
{
   SCON  = 0x50;
   TMOD |= 0x20;
   TH1   = 0xF7;
   TR1   = 1;
   PCON |= 0x80;
   TI    = 1;
}

    By the way, thanks for your interest in my problem :)

  • 0 in reply to Michael Gustafsson

    Okay, I think we're getting somewhere. Your problem is a good example why interrupt-driven and polling operation on a peripheral should not be mixed.

    I've added some comments to your code that should show what is happening.

    void uartInit(void);
{
   SCON  = 0x50;
   TMOD |= 0x20;
   TH1   = 0xF7;
   TR1   = 1;
   PCON |= 0x80;
   TI    = 1;
}


void main (void)
{
    int i=0;

    uartInit(); // This sets TI to 1

    // Global interrupt
    EA = 1;

    // Serial interrupt
    // Comment out below and printf in while will work
    ES = 1; // Since TI is 1, MCU will jump to UART ISR immediately

    while(1)
    {
        printf("..."); // printf will call putchar(), and putchar will enter an endless loop since TI is 0
    }
}

// The ISR function echos the received character
void serial_IT(void) interrupt 4
{
    if(RI==1)
    {
        RI=0;
        uart_data = SBUF; //Read received data
        SBUF = uart_data; //Send back same data on uart
    }
    else TI=0; // If TI was 1, then TI is set to 0
}