Hi Tengfei,
this is confusing. Lets make sure this is the right way.
For me the problem is how do we transform an HEX WORD to 16bits
for example can be interpreted from left to right as LSB and from MSB being
right to left when transforming the binary representation to the Hex
representation
Taking this IE as example
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
if we consider that E in 0x7E is the least significative 4bits and least
significative bits are placed first (most left) we have:
7 zeros 0x7e type 0
0000000011111100
1) When transforming this to HEX we consider the least significative bits to
go first from left to right. So
LSb MSb
0000 0000 1111 1100
0x0 0x0 0xF 0x3
0x00 0x3F
2) Another option is to convert to hex by considering the MSb first within
the octet
MSb LSb
0000 0000 1111 1100
0x0 0x0 0xF 0x3
0x00 0xFC
What is the right option? I am not sure but seems more reasonable to be 1)
Maybe those annexes in 15.4 can help to find the right answer.
regards,
Xavi
2015-06-23 17:33 GMT+02:00 Tengfei Chang <[email protected]>:
> Jonathan ,
>
> Could you pointed which annexes or a page I can refer to? Did it say that
> is an example that transmitted by PHY?
>
> Tengfei
>
> On Tue, Jun 23, 2015 at 11:27 PM, Jonathan Hui <[email protected]>
> wrote:
>
>> As mentioned in my previous mail, the annexes in the IEEE 802.15.4
>> specification use the convention I outlined.
>>
>> --
>> Jonathan Hui
>>
>>
>> On Tue, Jun 23, 2015 at 8:21 AM, Tengfei Chang <[email protected]>
>> wrote:
>>
>>> The hex value is correct. But I don't think this is the way to we should
>>> follow to order the data. IEEE802.15.4 said we should transmit the first
>>> bit, so we should follow this order.
>>>
>>> Tengfei
>>>
>>> On Tue, Jun 23, 2015 at 10:56 PM, Jonathan Hui <[email protected]>
>>> wrote:
>>>
>>>> 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
>>>>>>>>
>>>>>>>>
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>>>>>>
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>>>>>
>>>>
>>>
>>
>
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