[Tinyos-host-mote-wg] Re: [Tinyos-2.0wg] Timers in 2.x

[Philip Levis]

On Oct 18, 2005, at 3:23 PM, Joe Polastre wrote:

>
>> All of this is of course up to each platform, but I do think the
>> plethora of components is confusing to users...
>>
>
> That's why we have OSKI right?  The lower layers should be expressive
> and powerful, the upper layers abstract to a common interface,
> potentially with code bloat.

How do narrow top-level interfaces lead to code bloat? Building a can- 
do-everything service distribution will bring in lots of unwanted  
junk, yeah. But that's why there is no one-size-fits-all service  
distribution. If the components are structured properly, code size  
increases only come from increased functionality. Of course, this  
requires structuring them properly, something that we should do more  
carefully (*cough* init sequence *cough*).

The issue David G. is getting at is the difficulty of bringing up a  
new platform. For component granularity (if implemented well), is a  
tradeoff between efficiency and simplicity.  On one hand, I agree  
with him (and I'd be surprised if Cory didn't also) that the current  
decomposition is pretty complex and can be hard to understand.  
However, given how critical the timer system is, if that internal  
complexity is necessary to have a very efficient system, then I think  
it's OK in terms of the tradeoff. The question that David G. is  
raising is whether it can be made simpler without either sacrificing  
efficiency or flexibility. I personally don't know the answer to the  
question, but generally am of the opinion that Cory knows what he's  
doing.

There is also a question of what granularity of device we're  
optimizing for. The MSP430 is a really broad spectrum, with two  
orders of magnitude difference in RAM and almost two in code. Is it  
reasonable to think that there should be a completely general timer  
stack for the entire spectrum? Maybe what we need is chips/msp430 and  
chips/msp430lite.

The other option is to push more logic into platforms.

Phil
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