[Tinyos-host-mote-wg] Re: [Tinyos-2.0wg] Timer.fired

[Philip Levis]

On May 20, 2005, at 1:54 AM, Cory Sharp wrote:

> Okay, here's a even more simple counter proposal from talking with
> Joe, which boils down to "in this respect, go back to TinyOS1.x":
>
> 1) The timer subsystem assumes it can execute a periodic timer at the
> requested frequency
>
> 2) A periodic timer that falls behind will play catch up like TinyOS
> 1.x timer code, not compute skip-ahead like the TinyOS 2.x timer code
>
> 3) We drop direct support for "when" and "numMissed".  "when" can be
> computed from the gett0() and getdt() functions already provided.
> "numMissed" would not longer make sense.
>
> This makes more simple and smaller timer code by removing the integer
> modulus and integer divide used to calculate the skip-ahead.  For the
> MSP430, this saves 200 ROM bytes.  This also simplifies the Timer
> interface.
>
> I think this pulls back some of the over-engineering I was trying to
> do on the Timer interface and comes back to the basics.
>

Does this require more state (e.g., another byte for count)? It would  
seem to me that it would, but you tend to come up with crazy  
implementations that violate my cost assumptions. :)

I don't mean to say that another byte of state per Timer should  
preclude this approach. I just want to understand the tradeoffs.

Phil

-------

"We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time."

- T. S. Eliot,  'Little Gidding'

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