Re: [avr-gcc-list] How to calculate loops?

[Laszlo]

I'm going way out on a limb, since (ducking) I don't even have avr-gcc. 
I've done all my work in ASM so far. If (and I'm speculating here) 
_delay_loop_1() takes a 8 bit parameter and simply counts down clock 
ticks, you would be looking at a loop of about 3 clock cycles per count: 
one clock cycle for the DEC and [about] two cycles for the BRNE. So 
multiply that .25us period per cycle times 3 cycles per loop times the 
parameter passed in. Also, the very last BRNE check only takes one 
cycle, not two; So subtract one cycle at .25us from all of that.

_delay_loop_1(1)  = (.25us * 3 * 1)  - .25us = 0.5us
_delay_loop_1(69) = (.25us * 3 * 69) - .25us = 51.5us

If _delay_loop_1() is actually a subroutine (rather than a macro), add 
to that about another 7 cycles for the RCALL/RET.

If someone realizes I have no idea what I'm talking about, I'll gladly 
accept a good smacking-down. ;)

Laszlo

Johan Nilsson wrote:
> Hmm
> im using the avr-gcc _delay_loop_1(),  but where do i find how long time 
> it goes?
> if i use 4Mhz , and the AVR instuctions takes one cycle, how long 
> execution time does that instruction take?
> Does it take 0,25 mikroseconds?
> Can anyone explain this to me?

--
"That's the last time *I* answer to the name 'Sarah Conner'!" - me