Tengfei, Hex values are typically written in MSB order - this is different from IEEE 802.15.4 which writes bit strings out in LSB order.
For example: IEEE 802.15.4: 10000000 is equivalent to Hex: 0x01 So, w.r.t. the bytes being discussed: IEEE 802.15.4: 00000000 11111100 is equivalent to Hex: 0x00 0x3f See the Annexes in IEEE 802.15.4 to see many more examples of hex representations of MAC frames. -- Jonathan Hui On Tue, Jun 23, 2015 at 7:39 AM, Tengfei Chang <[email protected]> wrote: > I don't think 0x00 0x3F is right. > > In section 5.2 of IEEE802.15.4 standard, the second paragraph said : > > The frames in the MAC sublayer are described as a sequence of fields in a > specific order. All frame formats > in this subclause are depicted in the order in which they are transmitted > by the PHY, from left to right, where > the leftmost bit is transmitted first in time. Bits within each field are > numbered from 0 (leftmost and least > significant) to k – 1 (rightmost and most significant), where the length > of the field is k bits. Fields that are > longer than a single octet are sent to the PHY in the order from the octet > containing the lowest numbered bits > to the octet containing the highest numbered bits. > > When transmitting the data, we should make sure b0 goest first. > > > *For termination header IE * > *1) Header IE: list termination:* > *len = 0 as bits 0-6* > *id = 0x7e as bits 7-14* > *type = 0 as bit 15* > *header = len + id << 7 which gives 0x3f00* > > When transmitting the 00 3F, the bit transmitted by PHT is bit 7, not b0. > > => in the document, it is currently 00 FC: 0000000 01111110 0, > > The first 7 bits goes is len field bit0-bit6: 0000000, then goes ID: > b7-b14 7E 01111110, then type bit 15 0. > > Which is Correct. > > Tengfei > > On Tue, Jun 23, 2015 at 12:14 AM, Xavier Vilajosana < > [email protected]> wrote: > >> Dear Simon, >> >> thanks for your comments. I might have messed bits up with endianness. I >> will recheck again. Note that we read them from left to right being the >> leftmost the least significative bit and the right most the most >> significative bit. >> >> in this case and taking the first element you mention >> >> 7 zeros 0x7e type 0 >> 0000000011111100 >> >> if I convert this to hex where the least significant bit is the leftmost >> it leads to >> 0x00 0x3F >> >> as you indicate. >> >> thanks so much for your comment! >> X >> >> >> >> 2015-06-22 17:48 GMT+02:00 Jonathan Hui <[email protected]>: >> >>> As someone who has implemented and deployed product that use IEEE >>> 802.15.4e-2012 Information Elements, I agree with Simon's encodings. >>> >>> -- >>> Jonathan Hui >>> >>> On Mon, Jun 22, 2015 at 4:21 AM, Simon Duquennoy <[email protected]> >>> wrote: >>> >>>> Dear all, >>>> >>>> I believe the example IE headers (for header/payload/MLME IEs) are >>>> wrong in section 10.1 of the minimal draft. Some endianness confusion I >>>> guess: >>>> >>>> 1) Header IE: list termination: >>>> len = 0 as bits 0-6 >>>> id = 0x7e as bits 7-14 >>>> type = 0 as bit 15 >>>> header = len + id << 7 which gives 0x3f00 >>>> >>>> => with little endian encoding we get: 00 3F >>>> => in the document, it is currently 00 FC >>>> >>>> 2) Payload IE Header (MLME): 1A 88 seems correct >>>> >>>> 3) MLME-SubIE TSCH Synchronization: >>>> len = 6 as bits 0-7 >>>> id = 0x1a as bits 8-14 >>>> type = 0 as bit 15 >>>> header = len + id << 8 which gives 0x1a06 >>>> >>>> => with little endian encoding we get: 06 1A >>>> => in the document, it is currently 06 34 >>>> >>>> 4) MLME-SubIE TSCH Timeslot: >>>> len = 1 as bits 0-7 >>>> id = 0x1c as bits 8-14 >>>> type = 0 as bit 15 >>>> header = len + id << 8 which gives 0x1c01 >>>> >>>> => with little endian encoding we get: 01 1C >>>> => in the document, it is currently 01 38 >>>> >>>> and so on.. >>>> >>>> My apologies if it is me misreading something. >>>> >>>> One other minor remark: in section 10, when describing byte order, I >>>> would suggest referring to "little-endian ordering" rather than "LSB >>>> format". >>>> >>>> Thank you, >>>> Simon >>>> >>>> >>>> _______________________________________________ >>>> 6tisch mailing list >>>> [email protected] >>>> https://www.ietf.org/mailman/listinfo/6tisch >>>> >>>> >>> >>> _______________________________________________ >>> 6tisch mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/6tisch >>> >>> >> >> _______________________________________________ >> 6tisch mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/6tisch >> >> >
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