Comment by fabiensanglard

4 years ago

Thank you for noticing these issues, I have updated the table.

I would be happy to improve it and add encoding. I am surprised by some of the summary entries on Wikipedia (https://en.wikipedia.org/wiki/USB4). Looks like USB4 "reverted" to 128b/132b. It is accurate?

4 comments

fabiensanglard

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lxgr  4 years ago

128b/132b is the more efficient coding. The closer to 1 the fraction is, the less coding overhead it has, and 128/132 is larger than 8/10.

  • fabiensanglard  4 years ago

    Actually, I just noticed that 128/132 is the same fraction as 66/64 so both scheme has the same encoding efficiency. So USB-4 did no "revert in terms of efficiency.

    • masklinn  4 years ago

      Indeed, according to the wiki page the subtetly is:

      > USB 3.1 and DisplayPort 2.0 use 128b/132b encoding, which is identical to 64b/66b, but duplicates each of the preamble bits to reduce the risk of undetected errors there.

      I guess that was found not to matter so they went back to the more normal 64/66 in USB4? I'm really weak on the hardware stuff so I really have no idea.

Ldorigo  4 years ago

Fyi, last two columns in table 2 are a bit confusing: footnote c says "real life sequential speed", but then the last column title is "real life", so it's unclear what the difference is