Wakeup: sleep ; send to sleep nop ; after wakeup rjmp Wakeup
and
Wakeup: sleep ; send to sleep rjmp Wakeup
I mean, when the MCU woke up for some reason, where would the program point to go - to any interrupt vector entry, to the main portion, or to the "Wakeup" signed place in upper 2 codes?
js 
You may want to post some context.
An interrupt is required to wake the AVR. The AVR will call the isr of the interrupt that woke it up. What does the datasheet say?
And the ISR will return to the next line of code after the "sleep" statement.
nop may be desirable in some cases for things to "stabilize" after waking up. This will likely depend very strongly on the MCU and will certainly depend strongly on which of the several sleep modes is used. Thus, there is no universal answer about the nop.
Jim
You may want to post some context.
;
; *****************************************
; * Blink LED with timer at 128 kcs clock *
; *****************************************
;
.NOLIST
.INCLUDE "tn13def.inc"
.LIST
;
; ------- Register -----------------------
.def rmp = R16 ; multi purpose register
;
; ------- Timing -------------------------
; Internal RC oscillator = 128.000 cs/s
; Clock prescler CLKPR = 1
; Internal clock frequency = 128.000 cs/s
; TC0 prescaler = 256
; TC0 timer tick = 500 cs/s
; TC0 CTC divider = 250
; TC0 toggle frequency = 1 cs/s
;
; --------- Constants --------------------
.equ cCtc = 250-1
;
; --------- Programm ---------------------
; PB0 as output
sbi DDRB,DDB0 ; Port bit as output
; Timer Compare Match A to 250
ldi rmp,cCtc ; Match A value
out OCR0A,rmp ; to Match port A
; Timer as CTC and toggle output A
ldi rmp,(1<<COM0A0)|(1<<WGM01) ; Toggle and CTC
out TCCR0A,rmp ; to timer control port A
ldi rmp,1<<CS02 ; Prescaler to 256
out TCCR0B,rmp ; to timer control port B
; Sleep mode
ldi rmp,1<<SE ; Sleep mode idle
out MCUCR,rmp ; to universial control port
; Sleep loop
Wakeup:
sleep ; send to sleep
nop ; after wakeup
rjmp Wakeup
;
; End of source code
;
clawson 
It might have helped if you had simply made the link to the page where you got this:
http://www.avr-asm-tutorial.net/...
I'd suggest the person to ask is the person who wrote that code/article. I have a feeling the NOP may simply be there as an instruction to breakpoint on but perhaps the author will be able to tell you of some deeper reason he thought it was necessary ?
According to this linked page:
his email could well be:
info (ersetzen) gsc-da.de
I have a feeling that ersetzen may be the German word for the "at" symbol.
Shouldn't you at least toggle a pin to show yourself that it actually woke up? what are you hoping to do?
clawson
what are you hoping to do?
