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Re: what are the correct high/low maximums for _delay_ms()/_delay_us()

From: Britton Kerin
Subject: Re: what are the correct high/low maximums for _delay_ms()/_delay_us()
Date: Thu, 23 Jan 2020 13:38:06 -0900

On Thu, Jan 23, 2020 at 1:25 PM Joerg Wunsch <address@hidden> wrote:
> As Britton Kerin wrote:
> > I guess the high-res maximums are 262.14 ms / F_CPU in MH for
> > _delay_ms() and 768 us / F_CPU in MHz for _dalay_us() regardless of
> > the availability of __builtin_avr_delay_cycles(), but
> > the way the _delay_ms() and _delay_us() descriptions are written this
> > is not entirely clear.  Am I correct?
> I think you are.  They work beyond that now (has not always been the
> case) but lose a bit of accuracy/resolution.
> However, for the usual LED "I want 1 Hz" flasher, it's OK to have two
> _delay_ms(500) calls between turning the LED on and off.

Ok thanks.  I still think it's worth carefully documenting where the high/low
resolution threshold is for all cases though.  I was just trying to use the
_delay_us() to cross-check some timer1 code and confused myself a bit
not hitting the expected resolution due to crossing over the threshold.  In
my old age I'd probably make them separate functions as they're somewhat
overloaded as they are.


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