AVR Freaks

I'm so sorry dear Andy. I'll promise that I will do my best to be a good questioner and not irritating you. Your quickly answers make me lazy a little and I know it. I'll try to research first and ask if I can't solve my problems in research in next questions.

Thank you. 

I changed my program to this below program. 

#include <mega32.h>
#include <stdio.h>

int ring[500];
int head=0;
int tail=0;
int overflow=0;


interrupt [EXT_INT0] void ext_int0_isr(void)
{
    ring[head]=PINA;
    ++head;
    if (head==500)
       {
        head=0;
        overflow=1;
       }
}




void main(void)
{


// I remove all the configuration lines to make it easier to read here.

while (1)
      {
      if (tail<head)
        {
            printf("%02x",ring[tail]);
            ++tail;
        }
        
      if (overflow)
        {
        for(int i=tail;tail<500;tail++)
            {      
               printf("%02x",ring[tail]);
            }
            overflow=0;
            tail=0;
        }
      }
}

Is this methodology that I used equal to the same ring buffer?

Note that I reduce the rate of data transmission on DB4..7 line. It sends data for 1 second and wait 4 second and repeat it. 

Is there any problem?

And note that, between each 5 second delay, I receive 200 byte in the python output. So I think the size of ring is big enough for my program. Am I right?

Thank you dear friend. Your program works fine.  I just delete cli() and sei() from the program :D (My codevision detect errors in those lines.)

Let me to explain my program, please tell me what's wrong in my program :

This is my program :

#include <mega32.h>
#include <stdio.h>

int ring[500];
int head=0;
int tail=0;
int overflow=0;


interrupt [EXT_INT0] void ext_int0_isr(void)
{
    ring[head]=PINA;
    ++head;
    if (head==500)
       {
        head=0;
        overflow=1;
       }
}

In the ISR, I capture the RS and Data-Bus lines on each falling-edge of the En. if head==500 that means ring is full, so it starts from beginning of the ring and make an overflow-flag=1 instead. 

Now take a look at the main() loop :

void main(void)
{


// I remove all the configuration lines to make it easier to read here.

while (1)
      {
      if (tail<head)
        {
            printf("%02x",ring[tail]);
            ++tail;
        }
        
      if (overflow)
        {
        for(int i=tail;tail<500;tail++)
            {      
               printf("%02x",ring[tail]);
            }
            overflow=0;
            tail=0;
        }
      }
}

until tail is less than head, it sends ring[tail] to serial port and add tail by one.  it also check the overflow-flag in each loop. if the overflow-flag==1,  it means the tail must iterate to 499 instead of to head. (because head started agian from 0)

And why I think this program is OK? 
Because : I change the input of the ATMEGA8 in a way that it sends data/command to LCD for 1 second, and then waits 4 second and then again send data/command for 1 second and so on ...

In every 5-second I receive only about 200 character in sniffing. (In the other word, in that 1-second I capture only 200 character). This means that all the data that are transmitted in 5-second periods, are 200 character. and in the 4 seconds waiting, the buffer will empty! so, I don't loose any data with overwriting. right? I also capture all the data(because the length of them is 200 and is less than 500). is it right also?
So what the problem in this program?