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DHarmon

Dan Harmon back to talk some more about SuperSpeed USB.

Today I thought I would spend a little bit of time addressing the "other" benefits of SuperSpeed USB.

Most of the press activity around the technology has focused on the raw speed increase to 5 Gbps from the 480 Mbps of USB 2.0 High–speed, a over 10x increase.  But this is really only one of the four key values that the SuperSpeed USB Promoters were determined to deliver to the consumer.
• 10X Speed increase to 5 Gbps raw bit transfer rate
• Improving the power efficiency of the bus
• Maintaining backwards compatibility
• Improving the data transfer efficiency itself.

Improving power efficiency is ideal for extending the battery life for portable devices, whether hosts or peripherals. There are multiple aspects of the new specification that were developed to address reducing the overall power footprint of new USB devices including:
• Elimination of device polling
• Elimination of broadcasting packets
• Intermediate low–power IDLE states
• 10X data transfer speed increase
When you combine the bus usage efficiency (no broadcast packets and elimination of polling), the improved IDLE power states, and the lower average transmit power, SuperSpeed USB will consume approximately 1/3rd (or less!) the power of USB 2.0.

So what does backwards compatibility really mean then?  If we approach this from the end–user perspective, it means that ALL my existing products that are compliant to the specification will seamlessly connect to and work with all new products supporting the new specification!  This means that the existing cables (i.e. plugs) must be able to be inserted into the appropriate new receptacle.  The reverse is also true, that the new cables must be able to be inserted into the old receptacles – again where appropriate.

There are really two aspects to improving overall bus usage efficiency.  I have already touched on the first aspect of this: the elimination of polling - do not use the bus unless data is ready to be transfered.  In addition, the full duplex architecture of SuperSpeed USB allows for concurrent bi–directional data flow as opposed to the half duplex USB 2.0 architecture eliminating the need to "turn around the bus" which significantly cuts into bus efficiency.

Let me know how your products are taking advantage of these new benefits, Dan

 

Anonymous

  • Warren,

    Thanks for your comments.

    >> A pc-to-pc link via a usb3 cable.  Is it possible without some kind of active device, and special drivers? <<

    No, this is not something that the USB 3.0 specification enables.  SuperSpeed USB is still a master slave bus whose primary intent is connecting peripheral devices to a PC.  It only have a single host in any given bus tree.

    >> How about classless/driverless "just let me send bytes through this thing" uses? <<

    Anything you hook to a PC requires a driver to operate, even old RS-232 has a driver running on the PC.  The question is whether a driver is "native" or not.  Many devices utilize the HID class driver to just send data to/from the host, but they all require a driver.

    Thanks, Dan

  • What kills me is that we're up to 5 gpbs speed, but we still don't have the notion of RS232 "null modem" cables down.  A pc-to-pc link via a usb3 cable.  Is it possible without some kind of active device, and special drivers? How about classless/driverless "just let me send bytes through this thing" uses?  It's like the USB forum design people actively hate hobbyists, scientists, and people who just want something like RS232 that is a bit more up to date.   There's a reason most of us low-end project people use EzUSB chips. Because USB is a complexity nightmare.   Just look at the number of USB glitches on ARM eval boards.  It's a pandemic.

    Warren