Yup that's it... "packed". I was under the impression that the MSP chip was also little-endian (and that in fact just about every platform we use, save perhaps the Mac, is of that persuasion. If it's not able to access on odd boundaries (like our old favorite 68K's) then the nx_ translation code could get pretty wonky. But I think the nx_ types are defined big-endian so I guess the wonkyness continues no matter what...
This has to be about as far off the original topic as we can get, eh? MS Urs Hunkeler wrote: > By "pad/no-pad option" you mean the "__attribute__ ((packed))" compiler > attribute? Philip Levis in "TinyOS Programming" (e.g. > http://csl.stanford.edu/~pal/pubs/tinyos-programming.pdf) explains how > this works and why it should not be used. According to the above > referenced document, all fields in an nx_struct are aligned on byte > boundaries. So I guess this means the structure is "packed". > > I would expect the implementation of the nx_ types to be platform > dependent. If you look at the code for the MicaX platforms, there likely > is not much to see. However, the implementation for the Telos type of > platforms might be quite a bit more complex. Maybe this does not show in > the packet definition, but when accessing those variables, the code must > do something to change the endianness and to access 2-byte values that > are not aligned on 2-byte boundaries. > > Cheers, > Urs > > Michael Schippling wrote: >> I think the pad/no-pad thing is probably a compiler level feature >> and was most certainly for multi-byte objects on differing platforms. >> (The OP's struct had an int16-int8-int16, which on some platforms >> would have been layed out as int16-int8-padbyte-int16...or worse). >> Given that nx_ types are byte arrays they don't need it and are >> probably packed efficiently. Being an old guy I never trust that >> new-fangled stuff and thus avoid it...but thanks for the info. >> >> MS >> >> Eric Decker wrote: >>> >>> On Mon, Jan 12, 2009 at 11:17 AM, Michael Schippling >>> <[email protected] <mailto:[email protected]>> wrote: >>> >>> There "used to be" a pad/no-pad option especially for this. >>> Are the nx_ types defined to always be no-pad? >>> >>> >>> I've looked at the code generated and the nx_types are defined as >>> arrays of uint8_t. Not sure >>> how the pad no_pad used to work. I suspect it is for multibyte >>> objects such as uint16_t etc. >>> >>> But for the question originally asked int8_t were being asked about. >>> >>> eric -- Platform: WinXP/Cygwin TinyOS version: 1.x, Boomerang Programmer: MIB510 Device(s): Mica2, MicaZ, Tmote Sensor board: homebrew _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
