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Intel developer Sarah Sharp describes her work on USB 3.0 in her recent blog with these words: "Now that the bus specification is public, I can finally talk about the code... I've been writing a Linux driver for xHCI (the new USB 3.0 host controller), and changing the Linux kernel stack to support USB 3.0 devices." As she says, the wire speed will be 5 Gbps, while USB 2.0 languishes at 480 Mbps: "Roughly speaking, it means that a file that takes 30 minutes to transfer over USB 2.0 could take 3 minutes to transfer under USB 3.0."

In a video on her blog, Sharp demonstrates a USB 3.0 prototype from hardware provider Fresco Logic that runs under Linux. "My Linux xHCI driver is necessary to communicate with the USB 3.0 device through the xHCI host controller prototype," she adds. She was happy with the results: "The demo showed speeds that were about 3.5 times faster than USB 2.0 high speed devices. I expect this demo to be even faster when the device and host controller are implemented in silicon." The new bus also provides better power management that leads to longer battery life. And it is backward compatible so that you can continue to use it with USB 2.0 hardware.

Sharp asserts that USB 3.0 support for Linux means having to adapt the Linux USB stack to the new device speed and develop a new driver for the xHCI host controller. She is beginning the kernel patches for the USB changes and hoping that Red Hat, Novell and Ubuntu and other distros will begin picking them up. The work on the xHCI host controller will be a "little trickier," she says, because it is currently under a non-disclosure agreement as a 0.9 draft specification that isn't yet ready for Linux community review.

As much as basic USB 3.0 is there, "some features might be lacking. We might not have awesome power management right off the bat, or we might be missing USB 3.0 support from some class drivers," Sharp says, "My driver will be marked EXPERIMENTAL for a reason. ;)" Nevertheless, shipping code earlier and often (before it is "perfect") gives reviewers a better chance to suggest changes. Finally, she says that she's "willing to test new devices and host controllers on an unofficial basis to make sure they work properly under Linux” and provides her email address at Sarah.A.Sharp@linux.intel.com.

Microsoft is planning the new USB support for its upcoming Windows 7. According to Jeff Ravencraft, head of Intel's USB Promoter Group, the first USB 3.0 devices should start appearing the middle of 2009. The USB 3.0 specification is available here.

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