我在Atmel中编写AVR程序集，但是“调用”指令不起作用

Question

I'm using Atmel Studio 6.2 to write some assembly code for Atmega328p.

However, the call instruction for subroutine doesn't work when I use simulator and step-by-step execute the program. It completely ignores the call instruction and goes on to the next line.

In order to test the call instruction I wrote a simple program, which looks as follows:

.include "m328pdef.inc"

ldi R16, 11
call hello_world
mov R1, R0
nop

hello_world:
    mov R0, R16
    ret

But even this doesn't work! It just goes on to execute mov R1, R0 . What might be the reason? It's so annoying when call doesn't work!

Answer 1

.include "m328pdef.inc"
ldi r16,11 
ldi r17,0
ldi r18,1
rcall hello_world
mov r16,r17
nop

hello world:
mov r16,r18
ret

I am using r16,r17, and r18 because its general use registers, only use it for debugging.
here is the step by step explanation:
1. load immediate value "11" to r16
2. load immediate value "0" to r17
3. load immediate value "1" to r18
4. call hello_world label. push address into stack
5. move value from r18 (1) to r16, so r16 value is 1
6. ret, pop the address, and goes back
7. move value from r17 (0) to r16, r16 value is 0

If you run the program at once instead of step-by-step, you wont know the difference.
Hope this help

Answer 2

You have to define stack http://www.avr-tutorials.com/assembly/writing-assembly-subroutines-avr-microcontroller

;Initialize the microcontroller stack pointer
                LDI    R16, low(RAMEND)
                OUT    SPL, R16
                LDI    R16, high(RAMEND)
                OUT    SPH, R16