The common compiler technique is to silently pad fields to the natural boundary,
so probably the MPS gcc will stick a pad after a single byte to even things out.
I believe there are some compiler directives in TOS to control the padding, but
I've only used the micas so I haven't payed any attention.
I am a little surprised that what appears to be a base level define in message.h
has been changed in T2, I would have expected to see that happen in the platform
specific structs, maybe what Tie Luo sent was specific to telos motes.
...oh well...
MS
Jay Taneja 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
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