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Comment Re:Not a USB 3 problem (Score 1) 132

You probably won't break anything shorting D+/D- to Vbus or Gnd, but <0.3V signals SE0 reset on USB, and the voltage thresholds are set at 0.3V and 2.8V relative to Gnd. Ethernet permits common mode voltages of +/-20V and 40kHz (802.3 section 12.5.3.2.5).

Another interesting cable technology is MIDI, which was designed to connect instruments are are intentionally ungrounded. They use current signalling designed to directly drive opto-isolators!

Comment Re:Not a USB 3 problem (Score 4, Informative) 132

It's a shame that USB went with Vbus/Gnd rather than V+/V-. The latter would allow the negative side to drift away from ground (which is typically kept on the shield in a zero-current path). They had to devote a small section to voltage drops it in the latest spec (3.6.10.1 in USB_PS_R2_0 V1.1: bottom line is 375mV of Gnd rise and 625mV of Vbus drop).

The Ethernet guys realized this would be a problem so they made their signals transformer isolated. But USB is designed for short runs and cheap interfaces, not 100m runs across different electrical grids.

Note, however, that this case was not related to the ground potential at all. Vbus and Gnd were reversed, exceeding the Vgnd_drop limit by over 9V (2400%), or possibly 40V (>10000%) if the device had managed to negotiate the new voltage limits before it died.

Comment Re:huh, this is weird (Score 1) 140

Well, the IRS says the EIN was revoked (for non-filing of the 990) on May 15 2012. The Letter of Determination on X.org's site shows standing on May 17 2012 (and still current).)

Guidestar is often slow at finding 990s. If The Foundation filed its first return as the new 170(b)(1)(A)(vi) in Feb 2014 (extensions after first FY?) it may still be working its way through the system.

Still, the revocation is unusual, and cause for a second look.

Comment Re:so still not as complete as3.5 then? (Score 1) 111

I'll add a couple more things I miss (lost going from Kubuntu 14.10 to 15.10):

  • * Window titles on the side. I have a widescreen laptop, and having the window title bar on the side (rather than the top) of my windows was surprisingly useful. (I couldn't find an equivalent to the "bespin" widescreen theme. I'd do it myself if I could find a working theme editor, but after searching for an hour, I couldn't find a coherent description on how to theme Plasma5/Qt. The Bespin source code is a big horrible mess that I didn't want to port.)
  • * PDF preview in Dolphin file browser. An essential feature when you have hundreds of disparate PDF documents. It was apparently a Qt bug, and I hope it's fixed by now.

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