Re: XAUI/XGXS Question
Boaz,
The worst case XAUI/XGXS lane-to-lane skew anticipated is approximately 39 bits.
Skew sources included in this figure are described in:
http://grouper.ieee.org/groups/802/3/ae/public/mar00/taborek_1_0300.pdf, slide
16. The same slide indicates that the minimum distance between adjacent /A/'s is
160-bits. Since /A/ spacing is more than 4 times the worst case skew, there is
no ambiguity in determining which which /A/ code-groups are related.
The current proposal accounts for even the case of removal of all /R/ columns.
Performing deskew on the column including the Start-of-Frame delimiter requires
that both MAC devices transmit frames. This is not required for the current
proposal since /A/s are present in the IPG and in the absence of packets.
Best Regards,
Rich
--
Boaz Shahar wrote:
>
> Hi Rich,
> Recalling from your March presentation that the Max skew between two lanes
> is 8 Characters (80 bit), and that the distance between two adjacent /A/'s
> is 16 Characters.
>
> 1.So, in this case, how should one know Which /A/ is this? (That is, if a
> certain lane exceeds the other in 8 characters or delayed after the other in
> 8 characters it looks the same)
>
> 2.Suppose some /R/'s were dropped in the middle due to clock tolerance
> compensation. The result is that the distance between two adjacent A's is
> smaller than 16 characters. In this case its even more problematic to
> distinguish between delayed lane to an exceeding one.
>
> Can it be solved by:
> 1.Enlarging the gap between /A/'s
> 2.Doing de-skew on the /S/ and /Dxx.y/ code-words
>
> Thank you,
> Boaz
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