On Apr 26, 2009, at 12:40 AM, Benjamin M. Schwartz wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > John Watlington wrote: >> Quick straw poll on how many people think it is useful enough have >> individual >> control over the power supplied to each connector to raise the cost >> of the laptop >> by $0.15 ? > > Turning off a single port to which nothing is connected saves no > power, > right?
Correct. > I don't see the appeal. Maybe for deactivating power to passive > devices (e.g. usb sticks) during suspend, but such devices are > cheap to > power anyway, and may not shut down cleanly if their power supply is > killed. Moreover, I am persuaded by your argument that the > software is > unlikely to get smart enough to use it. > > Also, these "switches" are actually transistors, with some leakage > current > and some effective resistance, right? The leakage current is negligible (sub uA -- especially with nothing connected...) With a little design, you can get effective resistances around 22 milliohms for the price I mentioned (OK, maybe $0.18). This yields a loss of 6 mW (0.25%) at full rated power (0.5 A), and 22 mW (0.44%) at our rated power (1A through any connector). > So it seems like we pay for the flexibility of these switches with > a small > increase in power requirements. The price is the dominant factor. wad _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel