GCC will do one of two things: (1) pad (2) insert a uint8_t in the byte of extra space
Also note that the msp430 cannot write a word on non-word boundaries (ie, odd addresses). Back to the original question--it is 28 bytes on the CC2420 so that (1) space isn't wasted on 16-bit platforms and (2) interoperability between platforms. -Joe On 10/15/06, Jay Taneja <[EMAIL PROTECTED]> wrote:
I know that the Telos/Tmote implementations generally use 28 byte payloads because the 16-bit micro has some difficulties dealing with odd bytelength fields. The Mica family, on the other hand, has 8-bit micros. I am not quite sure of how exactly the MSP430 handles odd bytelength fields - it may just expand them by a byte so they are of even bytelength. Something to investigate... -jay On 10/15/06, Michael Schippling <[EMAIL PROTECTED]> wrote: > Ah, sorry, I should have said in tos 1.x it's 29. > I wasn't aware that it appears to be all different in v2. > > The main caviets are that longer messages have a higher > probability of getting a bit error which kills the whole > thing, and shorter messages have more header overhead. > Finding the right balance is of the essence. > MS > > > Tie Luo wrote: > > /opt/tinyos-2.x/tos/types/message.h:7:#define TOSH_DATA_LENGTH 28 > > /opt/tinyos-2.x/tos/chips/cc2420/CC2420.h:70:#define TOSH_DATA_LENGTH 28 > > /opt/tinyos-2.x/tos/chips/xe1205/XE1205.h:102:#define TOSH_DATA_LENGTH 28 > > I did not find anywhere defining it to be 29. > > > > p.s. If anyone point out the caveats of changing its value, I appreciate it. > > > > Tie > > > > On 10/15/06, *Michael Schippling* <[EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]>> wrote: > > > > Where did you find 28? The 'main' tos/types/AM.h file defaults to 29. > > And yes, you can change it. But search back on this list for caveats. > > MS > > > > > > Tie Luo wrote: > > > It can be found in TinyOS source code that TOSH_DATA_LENGTH is > > defined > > > to be 28, but I found in this mail archive people are saying 29, > > which > > > one is correct? > > > > > > Another question is, since 802.15.4 supports up to 127-byte > > packet, does > > > that mean we can redefine TOSH_DATA_LENGTH to be larger, say 100, as > > > long as the total packet size does not exceed 127? > > > -- > > > Regards, > > > Tie > > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > _______________________________________________ > > > Tinyos-help mailing list > > > [email protected] > > <mailto:[email protected]> > > > > > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > <https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help> > > > > > > > > > > -- > > Regards, > > Tie > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > _______________________________________________ Tinyos-help mailing list [email protected] https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
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