Posted by Eric Huang on August 8th, 2013
The 10 Gbps USB specification is now out and final.
Here’s what to call it.
- Enhanced SuperSpeed
- Gen 1 for 5G USB Physical Layer or PHY (formerly USB 3.0 or Superspeed USB that operates at all USB 3.0 speeds and lower) and
- Gen 2 for the faster 10G USB Physical Layer operating speed
- Together a complete PHY that operates at all USB speeds is called a Gen X PHY.
- SuperSpeedPlus when you are talking about the 10G only portions of the Link and Protocol layers (the controller)
For the purposes of this article, I’m going to call it 10G USB.
More Efficient Data Transmission
The PHY now uses 128b/132b encoding for 10G USB. This is a huge improvement over teh 8b/10b encoding.
For USB 3.0, the 5 Gbps standard, the 8b/10b encoding means that only 8 bytes of every 10 bytes transmitted are used for data transmission. Even though the PHY signals 5 Gigabits per second, the maximum throughput is only 4 Gigabits per second.
(We actually demonstrate that we can deliver this with our PHY and controller IP in this video from a thousand years ago below. )
But I digress. Going to 128b/132b goes to a 128 byte payload for each 132 bytes delivered. This improves the data efficiency from 80% up to 97%. So the signaling rate is faster, and the data efficiency is greater, so you can pump even more data through a standard USB 3.0 cable.
So the theoretical throughput of a 10G connection is 97% of 10 Gbps or about 9.7 Gbps. It’d be great if it was that easy to calculate wouldn’t it?
Which brings us to
In 10G USB, power hasn’t increased any further from USB 3.1, but remember that Power Delivery is the spec that already allows for power up to 100 W.
You can download the specification here.
What is the defined cable length for 10G USB?
Better question, what’s the defined length for USB 3.0 or USB 2.0 or USB 1.1?
The answer is: It’s not defined.
What is defined is the allowable “voltage drop”. This is dependent on the quality of the cable, connectors, and PHY. For 10G USB, the specification allows for 1 meter cable using the same standards for a USB 3.0 cable. The cable standards are the same because the USB-IF wants to keep the overall cost of the 10G USB and all USB cables down, or at least the same. Connectors are the same for USB 3.0.
Personally, I think this is okay because most 10G connections will be to either a USB flash drive, USB SSD, or a USB Monitor or docking station. In fact, I’m sure that something like 95% of cables sold are probably only 1 m today.
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Today we visit S&P 500 company that saved many months of engineering time using Synopsys USB PHY and core IP compared to alternatives. To me, this always means over an alternate IP supplier since it takes years to develop IP internally.
Read for yourself here.
USB Cables exist in 4 dimensional state
It’s even more funny when you realize we all exist in 4 dimensional space. Well, maybe someone can explain the joke to me in the comments section below.
Oh, and check out our PCIe Blog ExpressYourself. It’s written by two fine fellows who know more about PCIe that a Trained Monkey that plays the accordian. The most current entry using the M-PHY that we used in our USB 3.0 SSIC Demonstrations so take a look..