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Friday, September 21, 2012

Rubbing Sticks: Lighting The Kindle Fire

I recently obtained a Kindle Fire on which to experiment.  It was booted to the operating system and unlocked.  Naturally, I thought, "Enable USB Debugging and have a go at it with adb."  I looked at the settings and to my surprise: no USB debugging option!  A little research revealed that USB debugging is enabled by default on the Kindle Fire and it runs on a custom Android 2.3.  "Fantastic!" I thought, "This is going to be a piece of cake."

Dashed Hopes

Boy was I wrong.  It's not that the Kindle Fire is particularly hard to deal with, it's just very different from my normal Android experience.  Normally, for the Android Debug Bridge (adb) to connect to an Android device in Linux, the vendor ID needs to be defined in a udev rule.  A quick look at the vendor IDs listed on the Android Developer site reveals the definite lack of a definition for the Kindle.  So, how do we find one?
$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 004: ID 1949:0005 Lab126
The lsusb command displays information about USB buses on the system.  From the output, we see the vendor ID for the Kindle Fire is 0x1949.  Yes, that "Lab126" is the Kindle and yes, the ID is hexadecimal.  And in the event you were wondering, the second hex value after the colon, 0x0005, is the Prodoct ID.

False Hopes

OK, now we're in business, right?  I append the Kindle Fire to my android.rules file in /etc/udev/rules.d/ with the following lines:
#Amazon Kindle
SUBSYSTEM=="usb", ATTR{idVendor}=="1949", MODE="0666"
Now I start the adb server and read the device with:
$ adb devices
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
List of devices attached
Nothing!  How can that be?  I've added every new device in this way!  I should see the serial number of the device or at least a series of question marks (indicating I need to restart the server as root because I lack permission to read the device).

Discovering Fire

It took some poking around and some experimentation, but it turns out the only way I could get adb to see the Kindle fire was to add the Vendor ID to the adb_usb.ini file.  "An '.ini' file?  Isn't that for Windows?" you ask.  In a strict sense, an ini file is a text file used for application settings, and it is commonly found on Windows systems, but not exclusively so.

You may recall that when you installed the Android SDK, you launched the android application in the ./android-sdk-linux/tools/ directory.  When you selected and installed the "Android SDK Tools" and "Android SDK Platform Tools", a hidden .android directory was created in your user account, or in the root user account if you ran the tool as administrator (recommended).  In the directory is the adb_usb.ini file, which by default, or after an android update usb command, has the following content:
# cat /root/.android/adb_usb.ini
# ANDROID 3RD PARTY USB VENDOR ID LIST -- DO NOT EDIT.
# USE 'android update adb' TO GENERATE.
# 1 USB VENDOR ID PER LINE.
To connect to the Kindle Fire with adb, we need to append the Vendor ID, as a hexadecimal expression, to the adb_usb.ini file:
# echo 0x1949 >> $HOME/.android/adb_usb.ini
You can see the effect of your command with 'cat':
# cat adb_usb.ini
# ANDROID 3RD PARTY USB VENDOR ID LIST -- DO NOT EDIT.
# USE 'android update adb' TO GENERATE.
# 1 USB VENDOR ID PER LINE.
0x1949
Now, to connect the Fire, all that remains is to restart the adb server:
# adb kill-server
# adb devices
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
List of devices attached
0123456789ABCDEF device
Success!  

To recap, the udev rule does not help us in the case of the Kindle Fire.  The presence of the Vendor ID in the rule or lack there of has no effect on connecting to the device with the Android Debug Bridge in Linux.  The only effective method for connecting to the Fire is to place the Vendor ID in the adb_usb.ini file.

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