[Tinyos-devel] RE: [avr-gcc-list] Fwd: [Tinyos-help] TinyOs avr-gcc-4

[Philip Levis]

On Oct 15, 2007, at 2:30 PM, John Regehr wrote:

> Eric I'm not an authority on this topic but here are my two cents:
>
> - nesC adds plenty of value beyond facilitating inlining, for  
> example the
>   component model, support for concurrency, generic components,  
> network
>   types, etc.
>
> - I see no reason why nesC/TinyOS cannot use the latest and  
> greatest AVR
>   toolchain.  Probably it's mainly a matter of the TinyOS maintainers
>   finding time for toolchain work.  Also note that some TinyOS/nesC  
> ports
>   like msp430 are hopelessly mired in gcc3 for the foreseeable future.
>
> - David has spent a fair amount of effort on C interoperability for  
> nesC
>   programs.
>
> - nesC isn't that obscure, I think it can parse all of C.
>

Right -- nesC is a superset of C. If people wanted to, they can write  
a huge application as a bunch of C files which are #included into a  
single nesC component, and add some shims for downcalls/upcalls.  
People mostly don't, though, for a bunch of good reasons...

IIRC, the reason we haven't moved to avr-gcc v4 has to do with its  
interpretation of optimization parameters. Kevin looked a bit into  
this and found that -Os leads to huge code bloat, but that -O3 leads  
to similar results as is observed with -Os in 3.2/3.4. There was  
definitely talk of moving to avr-gcc 4 for the 2.1 release. But  
making this change requires more than compiling and seeing if code  
size is different; as far as we know, there might be weird compiler  
bug edge cases that nesC tends to tickle. So it would require a lot  
of testing. But I think that now might be a good time to get our feet  
wet. New Atmega MCUs are going to push this more and more as time  
moves forward.

Eric -- with respect to why it's not just a matter of changing to C,  
I suggest you take a look at the chapter of the TinyOS programming  
manual entitled "Namespaces." It's only about 10 pages of double- 
spaced text, so isn't a long read. It explains the fundamental  
limitations of C and why its namespace model fundamentally makes  
efficient composition difficult. TinyOS is, in part, an exploration  
of how modern (read, post-1970s) language and OS techniques can  
improve the robustness, maintenance, extensibility, and performance  
of embedded codes.

Phil