byte order of ethernet destination address
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Posted by on July 26, 2006, 11:31 pm
Please log in for more thread options Hi people, A simple and may be silly query for you. Can you tell me which byte of the ethernet destination address follows the start frame delimeter(SFD) on the gmii data bus....is it the byte 0(bits 7:0) or byte 6 (bits 47:39)? I think its byte 0 but want to make sure so please let me know. Thanks | ||||||||||||||||||||||
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Posted by glen herrmannsfeldt on July 27, 2006, 12:09 am
Please log in for more thread options pranavtailor@gmail.com wrote: The one on the left when you write the number on paper. Most likely the one at a lower address when stored in memory, as it will be the lower address in the output buffer. Some people, and some machine architects, number bytes in a word with 0 on the left, some with 0 on the right. Some are little endian, some big endian. -- glen | ||||||||||||||||||||||
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Posted by on July 27, 2006, 9:30 am
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Hi Glen thanks for the reply. So do you mean that the dest addr written as 48'hA2B012344567 on the paper will have the byte A2 showing up first followed BO, 12 and so on on the gmii data bus? glen herrmannsfeldt wrote: > pranavtailor@gmail.com wrote:
> > > A simple and may be silly query for you. Can you tell me which byte
> > of the ethernet destination address follows the start frame > > delimeter(SFD) on the gmii data bus....is it the byte 0(bits 7:0) or > > byte 6 (bits 47:39)? I think its byte 0 but want to make sure so please > > let me know. >
> The one on the left when you write the number on paper. > > Most likely the one at a lower address when stored in memory, as it will > be the lower address in the output buffer. > > Some people, and some machine architects, number bytes in a word with 0 > on the left, some with 0 on the right. Some are little endian, some big > endian. > > -- glen | ||||||||||||||||||||||
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Posted by Walter Roberson on July 27, 2006, 9:57 am
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>Hi Glen thanks for the reply. So do you mean that the dest addr
>written as 48'hA2B012344567 on the paper will have the byte A2 showing >up first followed BO, 12 and so on on the gmii data bus? The standards only talk about the transmission order once the data gets on to the transmission media. If for some reason you built your transmitter to buffer an octet at a time and transmit the octet in reverse order, then for consistancy the GMII data would have to be reversed as well. There are standards about GBICs and SFP's, so you wouldn't pull a trick like that if you were planning to use a -standard- GBIC or SFP, but it wouldn't be the first time that a manufacturer customized a transmission device to lock people in to their parts. | ||||||||||||||||||||||
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Posted by glen herrmannsfeldt on July 28, 2006, 5:39 am
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Walter Roberson wrote: >>Hi Glen thanks for the reply. So do you mean that the dest addr
>>written as 48'hA2B012344567 on the paper will have the byte A2 showing >>up first followed BO, 12 and so on on the gmii data bus? > The standards only talk about the transmission order once the
> data gets on to the transmission media. The MII for fast ethernet is part of the standard, and I thought GMII was also, though it rarely exists outside of the chips. In any case, that would be the expected ordering. -- glen | ||||||||||||||||||||||
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> of the ethernet destination address follows the start frame
> delimeter(SFD) on the gmii data bus....is it the byte 0(bits 7:0) or
> byte 6 (bits 47:39)? I think its byte 0 but want to make sure so please
> let me know.