[Tinyos Core WG] Unit of time in TOS2

[Cory Sharp]

On 10/20/06, David Gay <dgay42 at gmail.com> wrote:
>
>
> One comment: the introduction has a paragraph about accuracy which
> explicitly says that the timers may not be super accurate (i.e., that
> 1/1024s might well be 1/1000s anyway, the 1/32768s is definitely
> something else on mica family platforms). So worrying too much about
> the names doesn't seem that useful to me...
>
> Which does possibly bring up the question of whether we want to
> mandate better accuracy for TMilli... (but probably also a whole can
> of worms about drift, crystal accuracy, etc, that we may not care
> about...)
>
> David
>

Ah! Mandating accuracy for TMilli reminds me of our original plan (?) from a
year and a half ago.

1) Leave TMilli and TMicro as decimal names
2) Platform implementations may very well be off by ones of percent
3) Accuracy is not guaranteed by the TEP, anyway, because
3.a) Variations in hardware components between platforms
3.b) Clocks the internal clocks may significantly drift with
temperature/voltage, dwarfing the 2-5% binary/decimal variance

This brings us back to the network time and timers TEP -- if you really want
to say "millisecond" and have it mean something reasonably accurate, you
need to be synchronized with the network.  Those components and TEP do not
yet exist, but it's the right way to solve the problem -- building a timer
system built on synchronized timed.

The implication for TEP 102 is then we need to actually soften up the
language about "binary" units (though perhaps leave some discussion in there
about it), not strengthen in by renaming the precision tags.

Cory
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