RE: HARI: Question regarding byte (column?) versus word striping
> -----Original Message-----
> From: Mike Jenkins [mailto:jenkins@xxxxxxxx]
> I believe you are missing the point of how word striping works.
> As the number of lanes scales up, word striped data still uses
> ONLY ONE WORD to be added/deleted for clock tolerance compensation.
> That is, for n lanes, byte striping must delete n characters (ie,
> a column) while word striping must delete only 4 characters (ie,
> a word) from any one of the n lanes.
> Without the constraint that the packet begin in a particular lane,
> I believe that the IPG is CONSTANT for word striping, but must
> grow linearly with the number of lanes for byte striping.
> [Please note that the number of bytes (characters) in a "word"
> in word striping is chosen to span the expected skew, yielding
> its great simplicity of implementation. For HARI, it is merely
> coincidence that the word size is the same as the number of lanes.
> The word size and the number of lanes are independent things.]
I'm already having trouble with the idea that I have to create a
word stream clocked at 4x the speed of a link,
just to be able to cross my clock boundary. (Please reference my
previous e-mail of 06 Jan for details.)
Now you are saying that if the skew spec changes, I will have to
change the size of my internal data path. If I understand correctly,
the clock boundary transition is intended to be done at the word
size, whatever that may be.
I have a hard time understanding how this can be simpler. Column/byte
striped skew compensation does not seem like a picnic either, but
I believe a change there would impact state machines and buffer depths,
but leave my internal data path widths intact. Word striping would
seem to affect all three, in that case.
I am trying to think of ways to avoid having to create that word
stream... the problem is, the single idle word could appear on any
lane, and might -never- appear on a lane... anything I have been
able to think of (so far) has been too complicated for my taste.
Please help me understand what I am missing... thanks! - js
jeff stai, QLogic corp.
3545 harbor blvd, costa mesa, ca 92626