Touchscreen calibration in Android

Another how-to. This time about touchscreen calibration for Android.

We assume you already have your touchscreen driver for your dev board and you've tested it with Android getevent (or the evtest tool) and you're sure it's giving the right coordinates to user space.

Next step before really using it is calibration ... which is real pain in the a** because Android doesn't provide a calibration tool. For the purpose we are going to use ts_lib.

To clone ts_lib package ported for Android use:

$ git clone git://tslibonandroid.git.sourceforge.net/gitroot/tslibonandroid/tslibonandroid

Then build it as normal Android package with "mm" (I assume you already know how to build Android... If no checkout this link for basics).
Copy all output files from the build to their corresponding places in the target dev board.

To create calibration file for the touchscreen boot the board, export the following environment variables

export TSLIB_TSDEVICE=/dev/input/event1
export TSLIB_CONFFILE=/system/etc/ts.conf
export TSLIB_CALIBFILE=/system/etc/pointercal
export TSLIB_PLUGINDIR=/system/lib
export TSLIB_CONSOLEDEVICE=/dev/tty
export TSLIB_FBDEVICE=/dev/graphics/fb0

 (see also Android.mk in ts_lib sources)

and then run the newly built ts_calibrate tool.

Now we must apply this patch to make Android use the calibration file we created.

Rebuild Android services and you custom touchscreen must now work properly :) Hope it was useful!

P.S. the above was tested on Android Eclair with resistive touchscreen.
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Dropbear sshd on Android device

Recently I needed to have SSH connection with Android development board but since no SSH daemon is included in the official Android release I had some troubles finding the right way to do it.

The following guide was tested on OMAP3 development board with Android Eclair but should be working on any (rooted/unlocked) phone with Android.

Instructions how to run dropbear sshd on Android device:

First you fetch the latest Dropbear sources:

git clone git://android.git.kernel.org/platform/external/dropbear.git

Since the Android has different paths, no password support, etc. we must fix this in the original sources by applying the patch found here: http://pastebin.com/f3dedc5e7

...the only problem is that it's for older version of Dropbear so we must try to apply it manually :(

After patch was applied build with:

./configure --host=arm-none-linux-gnueabi --disable-zlib

make CC=arm-none-linux-gnueabi-gcc

In case you're unable to apply the patch correctly or something went wrong with the build here is a archive with prebuilt binaries (dropbear, dropbearkey, dropbearconvert):

>>> dropbear.tar.bz2

(Another guide how to build Dropbear for Android can be found @ http://teslacoilsw.com/dropbear)

Install:

To install dropbear on the desired gadget copy the binaries to some custom dir, e.g. /dropbear.

Setup the Server (Android):

Generate a RSA server key using dropbearkey:

dropbearkey -t rsa -f dropbear_rsa_host_key

Then create a dir /data/dropbear and copy dropbear_rsa_host_key there.

Test dropbear:

/dropbear/dropbear -r dropbear_rsa_host_key -F -E -v -s

This should show you the debuglog (the (-F) option means non-daemon mode).

Now we need to generate a key-pair for the client to connect with (Dropbear is run with the option -s (no-password) because there is no password support in Android):

//generates a private key

dropbearkey -t rsa -f /dropbear/id_rsa

//extract the public-key:

dropbearkey -f /dropbear/id_rsa -y > /dropbear/id_rsa.pub

We need to create /data/dropbear/.ssh and cat the public-key to authorized_keys:

mkdir /data/dropbear/.ssh

cat /dropbear/id_rsa.pub > /data/dropbear/.ssh/authorized_keys

IMPORTATNT: Check the perms of /data/dropbear and make sure they are *only* readable/writable by root!

Setup the Client (Ubuntu):

As dropbear and openssh use different key formats we first need to convert id_rsa (private key) to openssh-format:

./dropbearconvert dropbear openssh /dropbear/id_rsa /dropbear/id_rsa_openssh

Now move id_rsa and id_rsa_openssh to your desktop (e.g. to your home dir).

Before establishing connection gadget's USB interface should be UP:

busybox ifconfig usb0 up 192.168.1.2

(yes, busybox must be installed on the Android device...)

Finally connect to the device:

ssh -i id_rsa_openssh <device-ip>

You can use -vv for both the client and the server to see debug info and fix whatever is wrong.

Setup the Client (Windows XP):

The only difference is that we use different SSH client. I used PuTTY.

So...

- boot the board/phone

- connect PC with board with USB cable and wait for auto install

- set IP address (TCP/IP settings) in the automatically created USB Ethernet connection

- copy auth. keys generated with dropbear

- convert OpenSSH key to "PuTTY" key (ppk) using PuTTYGen

- open PuTTY and set remote IP/Port to connect to

- use SSH key generated with PuttyGen: Connection -> SSH -> Auth -> select key

- connect!

NOTE: The above is extended/edited version of the original guide @ http://cri.ch/sven/doku.php/blog/running-dropbear-on-android

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