= General =
Gen7 and gen8 Archos devices with resistive touchscreen use [http://www.ti.com/product/ads7846 TI ADS784x controller].

Stock Gingerbread doesn't support touchscreen calibration, TS range is simply scaled to screen resolution. To add calibration capabilities we use a [https://gitorious.org/openaos-cyanogenmod/device_archos/blobs/master/common/patches/frameworks/base/touchscreen_calibration.patch patch]. Calibration values are read from `/system/usr/idc/ADS784x Touchscreen.idc`, that defines 6 properties
{{{
touch.5pointcalib.xscale = 0.207832898
touch.5pointcalib.xymix = 0
touch.5pointcalib.xoffset = -24.934986945
touch.5pointcalib.yxmix = 0
touch.5pointcalib.yscale = 0.132637076
touch.5pointcalib.yoffset = -30.497127937
}}}
Screen coordinates are calculated as
{{{
Xscreen = xscale * Xtouch +  xymix * Ytouch + xoffset
Yscreen =  yxmix * Xtouch + yscale * Ytouch + yoffset
}}}
If the calibration file doesn't exist or any of the values is badly formatted, the system will scale TS range to screen resolution.

= Calibration Application =
Since static calibration values [http://dev.openaos.org/ticket/215 don't work for some devices], the app to define these values was made. 
== Building ==
Sources are hosted on gitorious [https://gitorious.org/touchscreen-calibrator]
{{{
cd device/archos/common
git clone git://gitorious.org/touchscreen-calibrator/touchscreen-calibrator.git
}}}
To build the app (assuming you are familiar with building openaos cyanogenmod)
Edit `device/archos/gen7/gen7.mk` (replace gen7 with gen8 if needed) and add `TSCalibrator` to `PRODUCT_PACKAGES` list. When you build the platform, the app would be built too and placed to `out/target/product/gen7/system/app/TSCalibrator.apk`.

Alternative way is
{{{
. build/envsetup.sh
lunch gen7-userdebug
make TSCalibrator
}}}

== Requirements ==
Since I (illifant) haven't found a way to get raw values from input device, the app uses existing calibration values, calculates correction and writes result to `/data/data/org.openaos.tscalibrator/files/ADS784x Touchscreen.idc`. For doing this, the system calibration file `/system/usr/idc/ADS784x Touchscreen.idc` must be world-readable.

If the file doesn't exist, calibration will start right after boot. To apply new values you have to reboot. The script [https://gitorious.org/openaos-cyanogenmod/vendor_archos/blobs/master/common/rootfs/system/xbin/apply_calibration.sh /system/xbin/apply_calibration.sh] will move newly written .idc file to the location in /system/usr/idc and make sure it's world-readable.