[laptop.org #1581] StopWatch activity

[Danny Clark]

So it doesn't look like there is consensus on this yet - Mako - since
you seem to be following this (and I'm at a conference), could you
ping me when you think consensus has been reached?

Thanks,
-- 
Daniel Clark # Sys Admin, One Laptop per Child
# http://laptop.org  # http://opensysadmin.com
# http://planyp.us/djbclark # http://dclark.us


On Nov 14, 2007 4:35 PM, Benjamin M. Schwartz <bmschwar at fas.harvard.edu> wrote:
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> Hal Murray wrote:
> >> Obsessive accuracy.
> > What's your version of "Obsessive"?  Seconds?  Milliseconds?  Microseconds?
> I have no desire to do better than 0.01s.  Human reaction times are an order of
> magnitude slower than that anyway.
> What I meant is, I have done everything I could think of to maximize accuracy,
> and this is obvious in the way the code is structured.  For example, the first
> instruction in each user-interface callback records the event time, before any
> processing is done, to minimize computation delay.
>
> > Are you assuming that the clocks on various XOs are synchronized?  If so, how
> > well?
> No.  Upon joining, a new member asks everyone else what time they think it is.
> The algorithm assumes that the network delay is the same in each direction.
> Whoever responds first "wins", because this computer experienced the least
> network+scheduling delay, and so the assumption is most likely to be true.
> Experimentally, this works very well with two nodes on a mesh; that's about all
> I can test at the moment.
>
> A more sophisticated synchronization algorithm would be appreciated, but I did
> not know how to make NTP work:
> 1. From python
> 2. As a highly restricted non-root user
> 3. Over Tubes
> 4. In a way that is resilient to the sudden disappearance of any member of the
> group.
>
> TamTam developers: I would like to know how you do synchronization.  I looked
> through your git repository, but I couldn't find any C source for it.
>
> > [Long discussion to follow in a separate messsage.]
> ?
>
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