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Thunderbolt Updates

March 20, 2014 by Steve Modica

We’ve been working pretty hard on Thunderbolt products over the last few weeks and I thought I’d write up some of the interesting things we’ve implemented.

I’m sure most of you are aware that Thunderbolt is an external, hotplug/unplug version of PCIE.  Thunderbolt 1 provided a 4X PCIE bus along with an equivalent bus for graphics only. Thunderbolt 2 allows you to trunk those two busses for 8X PCIE performance.

PCIE Pause

This is a new feature of Thunderbolt designed to deal with the uncertainty of what a user may plug in.

Normally, when a system boots up, all of the PCIE cards are in place. The system sorts out address space for each card and each driver is then able to map its hardware and initialize everything.

In the Thunderbolt world, we can never be sure what’s going to be there.  At any time, a user could plug in not just one device, but maybe five!  They could all be sitting on their desk, daisy-chained, simply waiting for a single cable to install.

When this happens, the operating system needs the capability to reassign some of the address space and lanes so other devices can initialize and begin working.

This is where PCIE Pause comes into play.  PCIE Pause allows the system to put Thunderbolt devices into a pseudo sleep mode (no driver activity) while bus address space is reassigned. Then devices are re-awakened and can restart operations.  What’s important to note is that the hardware is “not” reset.  So barring the odd timing issue causing a dropped frame, a PCIE Pause shouldn’t even reset a network mount on a Small Tree device.

Wake On Lan

We’ve been working hard on a Wake On Lan feature.  This allows us to wake a machine from a sleep state in order to continue offering a service (like File sharing, ssh remote login or Screen sharing).  This may be important for customers wanting to use a Mac Pro as a server via Thunderbolt RAID and Network devices.

The way it works is that you send a “magic” packet via a tool like “WakeonMac” from another system.  This tells the port to power up the system far enough to start responding to services like AFP.

What’s interesting about the chip Small Tree uses (Intel x540) is that it requires power in order to watch for the “magic” wake up packet. Thunderbolt wants all power cut to the bus when the machine goes to sleep.  So there’s a bit of a conflict here.  Does a manufacturer violate the spec by continuing to power the device, or do they not support WOL?

This is most definitely true for the early Thunderbolt/PCIE card cage devices.  They were all very careful to follow the Thunderbolt specification (required for certification and branding) and this leaves them missing this “powered while sleeping” capability.

Interested in learning more about how you could be using Thunderbolt? Contact me at smodica@small-tree.com.

 


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