avr learning 2 AVR assembler

When I first started learning about each CPU, I would first study the corresponding assembly instructions. I felt that this would allow me to quickly experience the hardware principles of the CPU, which would be very helpful for subsequent learning. Many people think otherwise, and feel that assembly is cumbersome and difficult to use. In fact, this will not give you a deep understanding of the internals of the microcontroller. Some basic assembly is very useful in single-step debugging, as well as scheduling writing, operating system porting, etc.

The following is an assembly program for making an LED flash. The comments are written in C, which is very clear.
**********************************************************************
//CPU: mega32
//Compiler: iar

        #include
        NAME main
        
        PUBLIC main
        
        ORG RESET_vect ; Reset interrupt vector
        RJMP main
        
        ORG INT0_vect ; External interrupt 0 interrupt vector
        rjmp eint0
        
main   

        ldi r16,0x99
        out DDRD,r16
        lds r1,DDRD
        cli
        ldi r16,high(RAMEND) ;get the high byte of the highest address of internal RAM
        out SPH,r16 ;put into the high position of SP
        ldi r16,low(RAMEND) ;get the low byte of the lowest address of internal RAM
        out SPL,r16 ;put into the low position of SP
       

        ;DDRD |= (1 << 7);//PD7 is set as outputin
        r16,DDRD
        sbr r16,1<<7
        out DDRD,r16
        
        
        ;eint0_init();
        call eint0_init
        
        ;sei();
        sei
        
        ;while(1);
        s: rjmp s
        
        
        ;#pragma vector = INT0_vect
        ;__interrupt void eint0(void) //INT0 interrupt service
        routineeint0:
        ;PORTD ^= 1<<7;//PD7 is invertedin
        r16,PORTD
        sbrs r16,7
        ldi r17,1<<7
        eor r16,r17
        out PORTD,r16
        
        reti
        
        
        ;void eint0_init(void)
        eint0_init:
        ;DDRD &= ~(1 << 2);//INT0 pin inputin
        r16,DDRD
        cbr r16,1<<2
        out DDRD,r16
        ;PORTD |= (1 << 2);//INT0 internal pull-up resistor is validin
        r16,PORTD
        sbr r16,1<<2
        out PORTD,r16
        ;SFIOR &= ~(1<         r16,SFIOR
        cbr r16,1<         out SFIOR,r16
        ;MCUCR |= (1 << ISC01) | (1 << ISC00);//INT0 falling edge triggerin
        r16,MCUCR
        sbr r16,(1 << ISC01) | (1 << ISC00)
        out MCUCR,r16
        ;GICR |= (1 << INT0);//Enable INT0
        in r16,GICR
        sbr r16,1 << INT0
        out GICR,r16
        
        ret

        END main
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