AVR, ATMega8, who is running his code on mine?

Hi,

I am wondering what happens here, like if code would run in the background
:-)


If I run this code (initialisation part being removed to clarify), PortB.2
remains low:

Timer0Overflow:
 reti

Reset:
 ...
 sei
 cbi PORTB, 2

Main:
 rjmp Main


And if I run following, PortB.2 goes low but immediatly after, et goes high
again (seen on my scope):

Timer0Overflow:

 cbi PORTB, 2
 reti

Reset:
 ...
 sei

Main:
 rjmp Main


In this second case the AVR behaves like if I would have cbi then sbi.
So, who is raising my PortB.2 output?

Regards

in fact, it seems it bahaves like if Reset occurs immediatly after
Timer0Overflow.
but I still do not know why.

looks it works much better if I initialize the stack pointer... sorry!


    ldi  R16, LOW(RAMEND)
    out  SPL, R16
    ldi  R16, HIGH(RAMEND)
    out  SPH, R16

    sei