[Tinyos-help] Precise contents and length of the 802.15.4 frames (and most especially with the TestNetwork App)

[Pedro Almeida]

Hey, Brian!

So that means it always is 28 bytes, regardless of being "filled" or not? So
if my struct is 1 or 28 bytes, the data bytes are always 28?

Thanks!


On 6/30/07, Brian Mulanda <bmulanda.tinyos at gmail.com> wrote:
>
>
> TOSH_DATA_LENGTH represents the max data payload; in your case, the
> struct. The size of
> the struct is allocated out of the 28 bytes.
>
> I am not certain of the total frame size; I think it is, coincidentally,
> at least 28 (13+15). In the event
> that escape bytes are included, to handle "reserved" bytes appearing in
> the data, it could be more.
>
> -Brian
>
> On 6/29/07, Pedro Almeida <pedralm at gmail.com> wrote:
>
> > Hello all;
> >
> > I would like to know the exact length of the 802.15.4 frame. The reason
> > that i'd like to know the exact length is because i need to do some duty
> > cycles numbers and one of the inputs is the frame length. It would seem to
> > equal the payload, but given it makes no sense to me the payload on the
> > serial frame, i might as well doubt i can figure the length on the
> > 802.15.4's.
> >
> > So according to TEP 125:
> >
> > The TinyOS 802.15.4 T-frame format is as follows:
> >
> > +-------------------+---------+------------------------------+--------------+
> > | 802.15.4 Header | AM type | data | 802.15.4 CRC |
> >
> > +-------------------+---------+------------------------------+--------------+
> >
> > I presume the 802.15.4 Header, as according to CC2420.h, to be 10 bytes:
> >
> > typedef nx_struct cc2420_header_t {
> > nxle_uint8_t length;
> > nxle_uint16_t fcf;
> > nxle_uint8_t dsn;
> > nxle_uint16_t destpan;
> > nxle_uint16_t dest;
> > nxle_uint16_t src;
> >
> > /** I-Frame 6LowPAN interoperability byte */
> > #ifdef CC2420_IFRAME_TYPE
> > nxle_uint8_t network;
> > #endif
> >
> > nxle_uint8_t type;
> > } cc2420_header_t;
> >
> > AM Type, according to previous struct, another byte before "data".
> > Total: 11.
> >
> > I suppose CRC to be 2 extra bytes added in the end. Total: 13
> >
> > The "data" field intrigues me.
> >
> > I see this being defined in CC2420.h
> >
> > #ifndef TOSH_DATA_LENGTH
> > #define TOSH_DATA_LENGTH 28
> > #endif
> >
> > Does this mean it's a fixed length that gets 'populated' according to
> > each different situation (making a fixed total of 42 bytes), or is 28 a max,
> > or am i understanding this all wrong?
> > The struct in TestNetwork is 15 bytes. Would that means the total frame
> > size is 13+15=28 bytes? Or is there anything extra added?
> >
> > Any help greatly appreciated!
> > Thanks,
> >
> > Pedro
> >
> >
> > _______________________________________________
> > Tinyos-help mailing list
> > Tinyos-help at Millennium.Berkeley.EDU
> > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
> >
> >
>
>
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