code not following the procedure

Question

I am currently working with ATTiny1634, executing the following code

After executing break statement the program is not exiting from the inner while loop to outer while loop; instead, it jumps to main function.

To test, I removed all the USART functions uart_init, writecommand, transmit, after removing all these function code is working perfectly.

The code works with ATMega16A, but getting problem in ATTiny1634. Why?

int main()
{   
    DDRC=1<<DDRC0;
    DDRA|= 1<<PORTA3;
    uart_init();
    sei();  
    writecommand("AT");

    writecommand("ATE0");
while (1)

  {
    int8_t t;
    PORTA=1<<PORTA3;
    // controller sleep mode
        if(MCUSR & (1<<WDRF))
        {
            MCUSR&= ~(1<<WDRF);
            WDTCSR|= 1<<WDE;
            WDTCSR= 0x00;
        }
        PORTA=0<<PORTA3;
        set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode selected
            //PRR=0X75;
            wdt_reset();
            WDTCSR |= 1<<WDE;           
            WDTCSR |= (1<<WDIE|1<<WDP3 |1<<WDP0); // ENABLE WATCH DOG TIMER INTERRUPT WITH 8S TIME OUT          
        sleep_enable();  //set SE bit   
        sei();  
        sleep_cpu(); //sleep mode activated

      while (1)
        {
         if(count >=2) // 80S DELAY
           {
            count=0;
            sleep_disable();   // SE bit reset
            WDTCSR|=0<<WDE|0<<WDIE; // disable watch dog timer
            transmit("AT+CFUN=1\r\n");
            _delay_ms(2000);            
            clearbuffer(buff);
            clearbuffer(temp_buff);
            _delay_ms(2000);
            break;
           }
         else
          {
            WDTCSR|=1<<WDIE;
            sleep_cpu();
          }         
        }

    }    

} 

The code for writecommand: void writecommand(char *q) {

    char str[3]="OK";
    char str1[50];
    do
    {
        clearbuffer(str1);
        strcpy(str1,q);

        i=0;
        _delay_ms(10);
        clearbuffer(buff);
        clearbuffer(temp_buff);
        transmit(str1);
        transmit("\r\n");
        _delay_ms(200);
        for(j=10;j>0;j--)
        _delay_ms(10);
        logic();   // my me
        clearbuffer(buff);        

    }while(strcmp(str3,str)!=0);    

I am using the 8 MHz internal osc and the baud rate in USART is 9600. Other functions are:

void uart_init()
{
    UCSR0B=(1<<TXEN0)|(1<<RXEN0)|(1<<RXCIE0); //transmitter enable,receiver enable,receive complete interrupt enable
    UCSR0C=(1<<UCSZ01)|(1<<UCSZ00);//8 bit data bits  
    UBRR0L=51; // baud rate 9600
}
void uart_send(unsigned char ch)
{
    while(!(UCSR0A &(1<<UDRE0)));
    UDR0=ch;
}
void transmit(char *p)
{
    i=0;
    while(*p!='\0')
    {
        uart_send(*p);
        p++; 
    }
}
void clearbuffer(char *p)
{
    while(*p!=0)
    {
        *p=' ';
        p++;
    }
}

Answer 1

Whenever you change from one processor to another, EVERY reference to a peripheral needs to be re-examined. Your code is a perfect example - it is full of Watchdog-specific code, and any change could cause the new processor to behave strangely.

Do you know what a Watchdog timer is? It is inside the controller, and its sole purpose is to reset the microcontroller back to the beginning of main(). That is all it does, and the only thing that can stop it is if the code "pats" the Watchdog before it times out. The idea is that you carefully structure your program so that it "pats" the Watchdog every so often - if it doesn't, then the code is bad and the microcontroller resets.

The code given even has a bug inside it:

    WDTCSR|= 1<<WDE;
    WDTCSR= 0x00;

This code carefully sets up bits inside the "WatchDog Timer Control/Status Register (WDTCSR)" - then zeroes it. Ummm... what?

In short, it is difficult to take existing code for one processor and simply execute it on a different one and expect it to work. Until you do, I would recommend that you comment out ALL code that references the Watchdog, until you get the rest of your code working.