I would like to understand how to configure ports (port, ddr, pin) using avr atmega328p Assembler

Question

Example that was testing, configure output ports and input ports, to be able to perform a sum, but are not working:

ldi r21, 0x0a
ldi r22, 0x0b

out PINB, r16
out DDRB, r16
out PORTB, r17

add r21, r22
mov r17, r21

Answer 1

1. A Nibble (half byte) is being loaded in R16. Normally the right is 0x0a or 0xa0.
2. 0xa0 in DDRB is equal to 0b10100000 which activates for output pins 7 and 5. While 0x0a is equal to 0b00001010 which activates for output pins 1 and 3.

3. To read a door door the correct is:

   In  r16, pinb