Warning: Attempting the following modifications to the NSLU2 can cause perament damage and will VOID your warranty. It is not yet known how this modification works exactly - proceed with caution and at your own risk! In addition, you can fry EVERYTHING on the USB bus if you manage to provide way more than +5v.
Based on recent work to automatically turn on the NSLU2, I've discovered a way to auto power a slug using USB only. I discovered it by using a cheap USB2? hub which can fetch power via USB using a special cable, in the same manner the 2.5" USB hard drives fetch power using a special cable. The schematic is attached below - can someone embed this?
For the DC power-source, I used a Belkin 12VDC adapter to USB (it plugs in the cigarette lighter of the car). Using a usb self-powered hub might work, but you're probably better of using something that WILL supply at least 1-2A of current such as the adapter that comes out of the NSLU2 itself(a self-powered hub will supply at most 500mA). Also remember by doing this you're bypassing any circuits designed to handle more than 5VDC SO BE ABSOUTELY SURE whatever you're using for DC supply will supply EXACTLY 5VDC, not 6VDC, not 12VDC or you WILL fry the USB controller.
Using a 12VDC to 5VDC adapter via USB has promising applications, such as powering the slug inside a car, (and an added benefit is that the slug will turn on automatically by itself when the car turns on!)
Also, powering your slug in this manner works so well that it WILL NOT TURN OFF if you use the power button. Only a disconnect of the USB cable will power down the slug!
Alternatively, you can just connect the +5V usb adapter header to the +5v and the GND lines on usb port 1, BUT I HAVE NOT TRIED THIS and this could possibly fry the USB2? controller (someone who has a clue about what they're doing try it out) .. it seems like it would work fine to me but maybe needs a diode.
<plasticmonkey/philipjohnson>: this needs a disclaimer *at the top* to explain that this way is not recommended for most people (eg: joe bloggs shouldn't do this without knowing what he is doing). Most of us are used to doing things like this, but I don't want to see a bunch of slugs returned back to Linksys because people have done this and fried/broken something.</me>
23/Oct/06:- I have found that connecting a single wire from the centre pin of the NSLU2 DC adapter socket straight to pin 1 on either of the USB sockets successfully makes the NSLU2 boot when the power is plugged in. I have done this mod to mine and it all works fine.
14/Dec/06: I finally have something to offer back to the community here. Before reading this, but after reading the bits on how to get my Slug(s) to auto power up I was particularly interested in the powering via USB. I extrapolated a little further as the editor above did about powering via the center pin on the slug power supply (on the PCB that is the one on bottom of the board that is even in depth from the edge of the board with the overall depth of the power connector). I have now soldered a wire from the center pin on the power connector to pin one on the first USB port (disk2). Pin one is the pin closest to the power connector on the PCB directly beside the "R94" marking on the board. I followed the trace back to an empty spot directly before the marking "R92" and above the "4" in "Q14". There I soldered the other end of the wire. While I was there I over clocked the Slug. I put it all back together and verified that it does boot. I have noted the failure to shut down / (update 2007/1/1) but the software does shut down with the confirmation beep, the Slug is inaccessible from the network and it is shutdown from a software perspective. / This should prevent the issue of providing over voltage, but I am open to anyone who might have other electrical concerns about why this is a problem. From the outside this looks stock. From the inside, it's one wire soldered in place. From my perspective it's an auto power up slug. / (Update 2007/1/1) I will also note that I have now modified my second Slug and will be moving on to the third this week. This seems to be a good solution for someone who is looking for a 24/7 slug with minimal effort/skill and no visual changes to the slug from the outside. /