hatsuseno's blog

Why not use the WiFi Hotspot

Recently HTC rolled out the Android 2.2 upgrade for my Desire, finally enabling USB Tethering out of the box. Often enough I used the WiFi hotspot feature on my previous phone to enable my laptop to have internet on the go. Android’s got this feature as well nowadays, but I don’t really like it because it really, and I mean *really*, puts the drain on your phone’s battery. USB Tethering seems like a much better solution.

Setup for Android

This is by far the easiest part, just hook up your phone, drag down the status bar and instead of charge only, or whatever mode it is in at that time, set it to USB Tethering.

Setup for Gentoo

This part is a bit trickier, especially when you roll your own kernel. Open up menuconfig for your kernel and enable these options

Device Drivers --->
  [*] Network device support --->
    USB Network Adapters --->
      [*] Multi-purpose USB Networking Framework
        <*> CDC Ethernet support
        <*> CDC EEM support
        <*> Simple USB Network Links (CDC Ethernet subset)
          [*] Embedded ARM Linux links
  [*] USB Support --->
    <*> USB Modem (CDC ACM) support
    <*> USB Wireless Device Management support

Now build your kernel as usual and reboot. When you now plug in your Android phone when it’s in USB Tethering mode, if all is well, you should be able to see a new network interface, usbX, X usually being 0. The link might be down, so check it with the command

$ ifconfig -a

Which will output something like this

usb0      Link encap:Ethernet  HWaddr 26:10:72:ab:38:0e  
            BROADCAST MULTICAST  MTU:1500  Metric:1
            RX packets:0 errors:0 dropped:0 overruns:0 frame:0
            TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000 
            RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

Which means it all worked. Now all you have to do is run a DHCP request on that interface, and Android will handle the rest. You can set up a init.d script for this interface much the same way you would for a normal interface. Just make a symlink from /etc/init.d/net.lo to /etc/init.d/net.usb0 and run that script whenever you want.

Beautifying the whole thing

Running around on the console starting bootscripts like that doesn’t suit everyone, including me when I’m just on the road and stuff needs to work. I recommend using something like wicd or NetworkManager to handle it for you. Using wicd it’s pretty easy to make it automagically use the usb0 interface when it appears, so you’ll only have to plug it on for it to work.