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AVR - ATmega8A - External Interrupt - Sometimes odd behaviour
von Alex K. (Company: ---) (akap)

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Hi,

I am currently working on a MCU unit which will respond to external 
interrupts in order to perform specific tasks. The controller I am 
using: ATmega8A.

The external interrupt is defined as followed:

1
PORTD |= 0x04;                //Activate pull up resistor of PD2

1
GICR |= (1 << INT0);          //Enable INT0

1
MCUCR |= (1<<ISC00);          //INT0 is executed on every edge


The ISR:

1
ISR (INT0_vect)

1
{

1
                /* interrupt code here */

1
                v = 1;          //sets interrupt variable v to 1

1
}


The variable v is defined as : volatile int v.

1
 volatile int v = 0;


I am currently testing the behavior of the external interrupts. Whenever 
an external interrupt is detected a particular code block should be 
executed. The interrupt is applied to the INT0 by any logic change.

1
 ISR (INT0_vect)

1
 {

1
     /* interrupt code here */

1
     v = 1;               //sets interrupt variable v to 1

1
 }

1
 int main(void)

1
 {

1
    USART_Init();

1
    I2C_init();

1
    //int a;                      //test variable

1
    PORTD |= 0x04;                //Activate pull up resistor of PD2

1
    GICR |= (1 << INT0);          //Enable INT0

1
    MCUCR |= (1<<ISC00);          //INT0 is executed on every edge

1
    sei();

1
    unsigned char a;

1
    a = USART_Receive();

1
 while(1)

1
    {

1
        //TODO:: Please write your application code

1
        do

1
        {

1
        } while (v == 0);     //Wait for interrupt

1
        v = 0;

1
        _delay_ms(10000);

1
  //Communication protocol between MCU unit and GUI software application

1
            //Block 1

1
            USART_Transmit(0xFF);                           //Header start command

1
            USART_Transmit(0x00);

1
            USART_Transmit(0x08);

1
            USART_Transmit(0x00);

1
            USART_Transmit(0x09);

1
            USART_Transmit(0x02);

1
            USART_Transmit(0x04);

1
            USART_Transmit(0x05);

1
            USART_Transmit(0x06);

1
            USART_Transmit(0x00);

1
            USART_Transmit(0xFE);                           //Header finish command

1
            do

1
            {

1
            } while (v == 0);          //Wait for interrupt

1
            v = 0;

1
        _delay_ms(10000);

1
 //Block 2

1
            USART_Transmit(0xFF);                           //Header start command

1
            USART_Transmit(0x00);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x00);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0x01);

1
            USART_Transmit(0xFE);                           //Header finish command

1
          }

1
     return 0;

1
 }

[c]

Testing the code, I can say that the interrupts are recognized and the 
code is functioning. However, it seems that there is a little bug or 
logic error. When the first interrupt occurs (before block 1), block 1 
is supposed to be executed. Now, if the second interrupt occurs, the 2nd 
block should be executed.

I can see this execution sequence in a pre-written GUI application, 
however, most of the time block 1 (when applying the interrupt) is 
executed many times after another and than block 2.

It should always be the following sequence: block 1 than block 2 and so 
on. I think that this is a timing issue. But I cannot debug this 
problem.

I am also wondering if there is a code in C that tells the program to 
wait for an external interrupt signal and than continues the program?

Thank you very much in advance.

  


  




  

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    Re: AVR - ATmega8A - External Interrupt - Sometimes odd behaviour
  


  

    

      von
      
        Marc Vesely (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

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Alex Kapphahn wrote:
> It should always be the following sequence: block 1 than block 2 and so
> on. I think that this is a timing issue. But I cannot debug this
> problem.

Is this now your complete code ( Except diverse #include etc.) ?
1
 

2
ISR (INT0_vect) 

3
{ 

4
                v = 1;          //sets interrupt variable v to 1 

5
} 

6
7
 volatile int v = 0; 

8
9
 int main(void) 

10
 { 

11
    USART_Init(); 

12
    I2C_init(); 

13
    PORTD |= 0x04;                //Activate pull up resistor of PD2 

14
    GICR |= (1 << INT0);          //Enable INT0 

15
    MCUCR |= (1<<ISC00);          //INT0 is executed on every edge 

16
    sei(); 

17
    unsigned char a; 

18
    a = USART_Receive(); 

19
20
 while(1) 

21
    { 

22
        do 

23
        { } while (v == 0);     //Wait for interrupt 

24
        v = 0; 

25
        _delay_ms(10000); 

26
  //Communication protocol between MCU unit and GUI software application 

27
  //Block 1 

28
            USART_Transmit(0xFF);                           //Header start command 

29
            USART_Transmit(0x00); 

30
            USART_Transmit(0x08); 

31
            USART_Transmit(0x00); 

32
            USART_Transmit(0x09); 

33
            USART_Transmit(0x02); 

34
            USART_Transmit(0x04); 

35
            USART_Transmit(0x05); 

36
            USART_Transmit(0x06); 

37
            USART_Transmit(0x00); 

38
            USART_Transmit(0xFE);                           //Header finish command 

39
40
        do 

41
        { } while (v == 0);          //Wait for interrupt 

42
        v = 0; 

43
        _delay_ms(10000); 

44
 //Block 2 

45
            USART_Transmit(0xFF);                           //Header start command 

46
            USART_Transmit(0x00); 

47
            USART_Transmit(0x01); 

48
            USART_Transmit(0x00); 

49
            USART_Transmit(0x01); 

50
            USART_Transmit(0x01); 

51
            USART_Transmit(0x01); 

52
            USART_Transmit(0x01); 

53
            USART_Transmit(0x01); 

54
            USART_Transmit(0x01); 

55
            USART_Transmit(0xFE);                           //Header finish command 

56
          } 

57
 

58
     return 0; 

59
 }

 If so, pls. post as such and not as bedsheet with unnecessary
 empty lines.
 Do you have TxBuffer ?

  


  




  

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    Re: AVR - ATmega8A - External Interrupt - Sometimes odd behaviour
  


  

    

      von
      
        Martin (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

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Try to use this instead of the _delay_ms(10000):

1
for (uint16_t i=0; i<=10000) _delay_ms(1);


The maximal possible delay is 262.14 ms / F_CPU in MHz.

When the user request delay which exceed the maximum possible one, 
_delay_ms() provides a decreased resolution functionality. In this mode 
_delay_ms() will work with a resolution of 1/10 ms, providing delays up 
to 6.5535 seconds (independent from CPU frequency). The user will not be 
informed about decreased resolution.

  


  




  

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    Re: AVR - ATmega8A - External Interrupt - Sometimes odd behaviour
  


  

    

      von
      
        Martin (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

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Martin wrote:
> for (uint16_t i=0; i<=10000) _delay_ms(1);

for (uint16_t i=0; i<=10000; i++) _delay_ms(1);

  


  




  

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