[Tinyos Core WG] TEP102 and binary vs decimal units

[Philip Levis]

On May 22, 2007, at 10:03 AM, Cory Sharp wrote:

> On 5/21/07, Philip Levis <pal at cs.stanford.edu> wrote:
> On Mon, 2007-05-21 at 16:05, David Gay wrote:
> > I'm finally getting to some final revisions for TEP 102, and the  
> only
> > real open issue is the "binary vs decimal" milli and micro second  
> one.
> > There's been a bunch of discussion on this, but I'm not clear we
> > really reached consensus. Two options:
> >
> > - Leave the current TEP 102 more or less as is, i.e., our units are
> > defined as 1/1024s, 1/32768s and 1/1048576s (TMilli, T32khz, TMicro)
> >
> > - Switch to the correspondiong decimal units (1/1000s, 1/32000s,  
> 1/1000000s)
> >
> > In practice, no implementations need change, as there's verbiage  
> about
> > accuracy being loose.
> >
> > FWIW, on mica platforms the actual units (w/o drift or temperature
> > effects) are 1/1024s, 1/28800s and 7.37/8000000s. On telos, I  
> believe
> > it's 1/1024s, 1/32768s and 1/1000000s.
> >
> > If nobody answers this week, I'll switch TEP102 to the decimal  
> units.
>
> The consensus was to stick with the binary units, with the  
> understanding
> that additional types could always be added for decimal units when/if
> needed.
>
> Phil
>
> I thought we switched to decimal units with the understanding that  
> there could be a reasonable inaccuracy in the unit, since there  
> will be in practice, anyway.  Essentially: if our error bars are  
> huge, we may as well pick a standard unit instead of making one up.

Is a 2% inaccuracy common? If not, then we should convert the calls  
to a best effort attempt at accuracy. I think it's disingenuous to  
say "they're decimal" but then give such a weak claim on accuracy  
that we make them binary. Doing this requires more bookkeeping of  
partial ticks, though, due to a need to keep timers in phase (e.g.,  
the simple (1000/1024) breaks if you ask for a periodic of 111ms and  
a periodic of 999ms).

Phil