Hi Urs, let me thank you for your clear response. now, i can see the difference much better. actually, the main reason i asked about "packed attribute" is that; i found a source code in tiny contrib ( TinyDiff application) where they use packed attribute. and i wonna use this code in order to implement the Directed Diffusion protocol but only for simulation purposes. and once i read the hint, i got confused.
i would like to reply to "Tiny User" about "having some experience with Tossim".... i am, actually, new either with tinyOS and Tossim. i am trying to implement a protocol using Tossim. so i am still learning. but we can help each other, just send your problem and i'll see if i (or someone else from the tinyOS Help list) can response. best regards. 2008/4/14 Urs Hunkeler <[EMAIL PROTECTED]>: > Hi Fatima, > > I think it's mainly a question of style. Often something starts as a > simple test, and then all of a sudden the code is in some production release > and everybody has forgotten about the little hack for testing purposes. > > Then again, why would you need the packet attribute anyways? The only > reason I see for using the packet attribute (on TinyOS 1.x) is to actually > ensure that all platforms put the data bytes at the same offset when > transmitting data. So if you only use one platform (simulation), then the > packed attribute is not necessary, and if you use multiple platforms > (testing on real hardware) you should not use it :-) > > Cheers, > Urs > > > fatima zohra wrote: > > > hello, > > thanks for both of you for your reply. > > however, i'm still confused. > > actually my code will be use for simulation with Tossim; i have no real > > motes to implement. so, there is no precised platform to use. > > is it still a problem to use this "packed attribute" only for simulation > > purpose? > > > > Best Regards. > > > > 2008/4/14 Urs Hunkeler <[EMAIL PROTECTED]>: > > > > Hi, > > > > > > I thought that the compiler for the MSP430 architecture would simply > > > ignore the packet attribute. > > > > > > Even if the code executes on the motes, some compilers might ignore > > > the > > > packet attribute. This results in the packet format not being equal on > > > all > > > platforms, essentially meaning that motes from different platforms > > > cannot > > > communicate. > > > > > > In TinyOS 2.x the nx_ types were introduced (like nx_uint8_t) that > > > should > > > be used for packet structs. The nx_ types ensure the same endianeness > > > and > > > the same data packing for all platforms. > > > > > > Cheers, > > > Urs > > > > > > > > > Philip Levis wrote: > > > > > > On Apr 13, 2008, at 7:32 AM, fatima zohra wrote: > > > > > > > > hello, > > > > > while reading the TinyOS programmation manual here, i came across > > > > > this important Hint : > > > > > > > > > > Programming Hint 14: Never, ever use the "packed" attribute. > > > > > > > > > > > > > > > can anyone explain to me why is it so important to notice this > > > > > problem ?? is it a big issue if we use packed attribute ? > > > > > > > > > > Because if you used the packed attribute, words will not > > > > necessarily be > > > > aligned on word boundaries. Some architectures (such as the MSP430 > > > > of Telos > > > > nodes) require words be aligned on word boundaries, or return > > > > undefined > > > > results. So if you use the packed attribute, you could have code > > > > that > > > > cannot work correctly. > > > > > > > > Phil > > > > > > > > > > >
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