what is the field uint16_t fcf; ? On 7/1/07, 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:468761d4237032051017194! _______________________________________________ Tinyos-help mailing list Tinyos-help@Millennium.Berkeley.EDU https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
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