Thank you once again, Steve, you're a tireless help! =)
I guess I found strange the concept of something being included in a message
structure that never gets to be sent...
On 7/3/07, Steve McKown <[EMAIL PROTECTED]> wrote:
On Tuesday 03 July 2007 11:01:48 am Pedro Almeida wrote:
> All,
>
> Ok, I'm intrigued again... (why does this keep happening??)
>
> [snip]
>
> From the same TEP, "The metadata field of message_t stores data that a
> single-hop stack uses or collects does not transmit. This mechanism
allows
> packet layers to store per-packet information such as RSSI or
timestamps."
> [snip]
>
> So some questions rise:
> 1 - Is the metadata actually carried out in the message being sent over
the
> radio and actually included in the message_t (cause it says something
about
> not being transmitted, but it still show up in the message structure in
the
> TEP)?
You just quoted from the TEP that answers your question. ;^) message_t
stores metadata that the stack uses or collects but does not transmit.
> 2 - If it is, does the actual size of the 802.15.4 message payload
> (Data field) extends by its size (after sizeof(struct) as we've seen
> before)? How many bytes then? 7 or more?
> 3 - If it's not.. what use does it have?
The metadata is useful for writing network functionality. It's used in
CTP
for example, to manage neighbors and routing. I don't think you'd want an
application to use metadata directly, since you're then tying that
application to a specific bit of radio hardware.
>
> Thank you and continuous apologies on my behalf,
>
> Pedro
>
> On 7/2/07, Steve McKown <[EMAIL PROTECTED]> wrote:
> > On Saturday 30 June 2007 06:35:32 pm Pedro Almeida wrote:
> > > Hello, Steve!
> > >
> > > Wow, that was a very thorough and explicit explanation, i'm all
cleared
> > > now! Only in
> > >
> > > Radio Frame = SHR(5) + PHR/len(1) + MHR/addr(8) + AMtype(1) +
> > > AMdata(TOSH_DATA_LENGTH) +
> > > CRC(2)
> > >
> > > you mean 9 in the MHR, right?
> >
> > Dang. Yeah. Thanks for catching that!
> >
> > > MHR = FCF(2B) + DSN(1B) + PANID(2B) + DST(2B) + SRC(2B) = 9
> > > (note that PANID is populated by TOS_AM_GROUP)
> > >
> > > So it's TOSH_DATA_LENGTH + 18 instead of 17. Making the size = 46
> > > bytes.
> > >
> > > Just as a final clearance: the length supplied to AMSend.Send() is
> >
> > directly
> >
> > > related to TOSH_DATA_LENGTH, so regardless the size of the struct
being
> > > sent is 1 or 20 bytes, the payload length is that of defined by
> > > TOSH_DATA_LENGTH, correct? I cant have a payload smaller than
> > > TOSH_DATA_LENGTH?
> > >
> > > Thank you so much, I believe your reply might come in handy for more
> > > people! Once again many thanks,
> > >
> > > Sincerely,
> > >
> > > Pedro
> > >
> > > On 6/30/07, Steve McKown <[EMAIL PROTECTED]> wrote:
> > > > On Saturday 30 June 2007 09:34:39 am Pedro Almeida wrote:
> > > > > Hi, Erwing;
> > > > >
> > > > > I've taken a good look at the data sheet. I've looked at it
before
> >
> > but
> >
> > > > > I totally forgot the details from seeing just the TEP and the
> > > > > header
> > > >
> > > > files.
> > > >
> > > > > according to the sheet, total PPDU frame is:
> > > > >
> > > > > PPDU = SHR (5 bytes) + PHR (length: 1 byte) + MPDU
> > > > >
> > > > > now the MPDU starts with the rest of the struct (apart from the
> > > > > length):
> > > > >
> > > > > 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;
> > > > > nxle_uint8_t type;
> > > > > } cc2420_header_t;
> > > > >
> > > > > MPDU = FCF + DSN + DestPAN + DestAdd + SRC + FCS = 11 bytes
> > > > >
> > > > > Total so far : 11 + 6 = 17
> > > > >
> > > > > The "type" I don't know where it belongs, maybe the start of the
> >
> > data
> >
> > > > > payload? It does say in here:
> > > > >
> > > > > The TinyOS 802.15.4 T-frame format is as follows:
> >
> >
+-------------------+---------+------------------------------+-----------
> >
> > > >--
> > > >
> > > > >-+
> > > > >
> > > > > | 802.15.4 Header | AM type | data | 802.15.4 CRC |
> >
> >
+-------------------+---------+------------------------------+-----------
> >
> > > >--
> > > >
> > > > >-+
> > > > >
> > > > > so should be "somewhere" between the Header and the data.
> > > > >
> > > > > Anyway, the "data" field i still dont know if its size is the
exact
> > > > > size
> > > >
> > > > of
> > > >
> > > > > the struct i'm using, if there's some more bytes added or if it
is
> > > >
> > > > always
> > > >
> > > > > defined by the MAX setting, regardless of being filled or not.
> > > > >
> > > > > Finally, the CRC in the scheme above, i dont know if its the
same
> > > > > as the FCS (as the FCS is only from the MPDU) or if after the
FCS,
> > > > > 2
> >
> > CRC
> >
> > > > > bytes actually are inserted (extending actual size to another 2
> >
> > bytes).
> >
> > > > You're close. It's a bit confusing because the 802.15.4 spec
breaks
> >
> > up
> >
> > > > the
> > > > radio frame into 3 layers, and in t2 the length field in
> >
> > cc2420_header_t
> >
> > > > is
> > > > not part of the MPDU but is in fact the PHR. Here's how I
understand
> >
> > t2
> >
> > > > active messages on 802.15.4:
> > > >
> > > > The physical protocol data unit (PPDU), or the actual bytes that
make
> >
> > up
> >
> > > > the
> > > > full radio frame are:
> > > >
> > > > PPDU = SHR(4B preamble + 1B SFD) + PHR (1B len) + PSDU
> > > >
> > > >
> > > > The phy service data unit (PSDU) contains the mac protocol data
unit
> > > > (MPDU),
> > > > so they are synonmous:
> > > >
> > > > PSDU = MPDU = MHR + MSDU + FCS(2B)
> > > >
> > > >
> > > > The mac header (MHR) is variable based upon bits set in the
FCF. For
> >
> > the
> >
> > > > t2
> > > > stack it is 8 bytes long:
> > > >
> > > > MHR = FCF(2B) + DSN(1B) + PANID(2B) + DST(2B) + SRC(2B)
> > > > (note that PANID is populated by TOS_AM_GROUP)
> > > >
> > > > The frame check sequence (FCS) contains the CRC and is 2 bytes
long.
> > > >
> > > > The mac service data unit (MSDU) contains the data payload. For
> >
> > active
> >
> > > > messages, this is the AMtype field and a variably sized AMdata
field.
> > > > The AMdata field contains the payload of the message_t sent to
> > > > AMSend.send(), whose length is another argument to the same
> >
> > AMSend.send()
> >
> > > > invocation. The
> > > > maximum size of the data field is defined by TOSH_DATA_LENGTH:
> > > >
> > > > MSDU = AMType(1B) + Data(<= TOSH_DATA_LENGTH bytes)
> > > >
> > > >
> > > > So putting it all together, for t2 active messages on the cc2420
> >
> > radio,
> >
> > > > the
> > > > radio frame looks like this:
> > > >
> > > > SHR(5) + PHR/len(1) + MHR/addr(8) + AMtype(1) +
> >
> > AMdata(TOSH_DATA_LENGTH)
> >
> > > > + CRC(2)
> > > >
> > > > If I haven't fouled up somewhere, the maximum size of the radio
frame
> >
> > is
> >
> > > > TOSH_DATA_LENGTH +17 bytes, or 45 bytes using the standard
definition
> >
> > for
> >
> > > > TOSH_DATA_LENGTH. The actual size of a particular radio frame is
len
> >
> > +
> >
> > > > 17 bytes, where len is the length parameter supplied to
> > > > AMSend.send()..
> > > >
> > > > All the best,
> > > > Steve
> > > >
> > > > > Thanks for the help!
> > > > >
> > > > > Pedro
> > > > >
> > > > > On 6/30/07, Erwing Sánchez <[EMAIL PROTECTED]> wrote:
> > > > > > Hi Pedro,
> > > > > > you may want to take look to the cc2420 datasheet. I found a
lot
> >
> > of
> >
> > > > > > useful information regarding IEEE 802.15.4 there!
> > > > > > www.chipcon.com/files/CC2420_Data_Sheet_1_3.pdf
> > > > > > Or you may want to try the IEEE 802.15.4 standard, where you
can
> > > > > > certainly find all this information.
> > > > > > Take into consideration that, for instance, the length of the
> >
> > frame
> >
> > > > > > Header varies according to the value of the fcf field (I think
> >
> > most
> >
> > > > > > of the time it is not changed in TinyOS applications).
Besides,
> >
> > the
> >
> > > > > > frame length changes in accordance to the application because
the
> > > > > > payload changes.
> > > > > > However, If you're looking for maximum values, the maximum
frame
> > > > > > length is 128 bytes in 802.15.4.
> > > > > > Regards,
> > > > > > Erwing
> > > > > >
> > > > > > On 6/30/07, Pedro Almeida <[EMAIL PROTECTED]> 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@Millennium.Berkeley.EDU
> >
> >
https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>
> !DSPAM:468a8241248535260519334!
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