[Tinyos-2.0wg] msp430 usart configure

[Philip Levis]

On Aug 4, 2006, at 8:35 AM, Jonathan Hui wrote:

>
> Okay, makes sense. I did measure directly the overhead and it takes  
> less than 10us extra processing time and setModeSpi uses about 90  
> bytes more overhead, so I guess it's not that much overhead.

Actually, let's think about this for a moment. 10us is how many  
cycles? 40 or 80? That's actually not insignificant: the latter is  
about the same as a task queue post/run, so essentially doubling the  
overhead of an ownership transition. While a lot of the operations in  
TinyOS are infrequent enough that we've never really worried about  
fine-turning performance, this is a really low-level mechanism that's  
used all over the system (like tasks). It might therefore be  
worthwhile to try to optimize it, or at least not codify an interface  
which is inherently inefficient. While I might buy 10% overhead for  
the simplicity that consistency brings, 100% overhead seems a bit  
much...

Phil