Linux Touch Screen HOWTO

Linux Touch Screen HOWTO

(c) 2002 by Christoph Baumann, cgb@debian.orgv2.1, Jan 11, 2002

This document describes how to set up a touch screen input device under XFree86. As the author had only the opportunity to work with devices from !EloTouch?(R) and !MicroTouch?(R) this HOWTO is rather specific for these devices.

The GNU Free Documentation License applies to this document.

1. Which sort of devices are described here?

2. How to configure the device

3. Activating the device

4. Using touch screen and mouse in parallel

5. Configuration under XFree86 4

6. Suggested reading

1. Which sort of devices are described here?

This HOWTO concentrates on devices connected via the serial port i.e. /dev/ttyS0 or /dev/ttyS1.

2. How to configure the device

Touch screen devices are configured in the Xinput section in the XF86Config file (mostly /etc/X11/XF86Config or /etc/XF86Config). At first verify that the device driver modules exist. They are located in /usr/X11R6/lib/modules/ (the modules for the above mentioned devices are xf86Elo.so and xf86MuTouch.so). Now have a look into XF86Config. There should be a section looking like this:

Section "Files" ...

ModulePath? "/usr/X11R6/lib/modules"

...

EndSection?

To get the module loaded by the X server there has to be a section like this:

Section "Module" Load "xf86Elo.so"

EndSection?

Now the more tricky part. X needs to know some parameters about the device. The section for this looks like this (see "man XF86Config" for more details):

Section "Xinput"

SubSection? "Elographics"

1. the entry for a !MicroTouch? device would be !SubSection? "!MicrotouchFinger?"

Port "/dev/ttyS1" # for a device at serial port 2

DeviceName? "!TouchScreen?" #could be any unambiguous name

MinimumXPosition 300 MaximumXPosition 3700 MinimumYPosition 300 MaximumYPosition 3700

UntouchDelay? 10 #not supported with !MuTouch?

ReportDelay? 10 #not supported with !MuTouch?

AlwaysCore? #activates the device on startup

EndSubSection?

EndSection?

The values for the entries MinimumXPosition etc. are of course specific for the setup of the hardware (i.e. depend on the position of the touch screen relative to the monitor). The values determine where the points (0,0) and (xmax,ymax) on your monitor (xmax and ymax depend on the resolution chosen for the Xserver, such as 1024x768) are mapped on the touch screen. The device driver reads these values and interpolishes the other coordinates. For illustration:

--------------touch screen area----------------- I I I ########visible monitor area############## I I #x # I I # (0,0) # I I # (MinimumXPosition,MinimumYPosition) # I I # # I I # # I I # # I I # # I I # # I I # # I I # # I I # (MaximumXPosition,MaximumYPosition)# I I # (xmax,ymax)# I I # x# I I ########################################## I I I

This mapping can be done by trial and error or by reading the raw output of the device (needs some serial port programming, see "The Linux Serial Programming HOWTO"). For the types !EloTouch? and !MicroTouch? exists a rudimentary calibration tool (written by the author of this document, it can be found at ftp://metalab.unc.edu/pub/linux/X11/xutils/touchcal-0.1.tar.gz).

3. Activating the device

After starting X, type in an Xterminal the command

xsetpointer <devicename>

where<devicename> is the name defined in XF86Config with the line

DeviceName? ".....", in this example it would be !TouchScreen?.

To get the device working on startup use the !AlwaysCore? option in the touch screen section (see above)

4. Using touch screen and mouse in parallel

To use the touch screen and a mouse in parallel you need to enter the mouse specs in the Xinput-section. This definitions should be the same as in the Pointer-section. The following example is for a PS/2-mouse:

Section "Xinput"

SubSection? "Mouse"

Protocol "PS/2" Port "/dev/mouse" #could also be /dev/psaux

DeviceName? "Mouse"

AlwaysCore?

EndSubSection?

...

EndSection?

Several people pointed this out, especially the usage of the

AlwaysCore? option. Thanks to them all.

5. Configuration under XFree86 4

(from Lee Monamy)

Example XF86Config-4 for an ELO touch screen:

Section "!InputDevice?" Identifier "ELO touchscreen" Driver "elographics" Option "Device" "/dev/ttyS0" Option "MinimumXPosition" "300" Option "MaximumXPosition" "3700" Option "MinimumYPosition" "300" Option "MaximumYPosition" "3700" Option "!UntouchDelay?" "10" Option "!ReportDelay?" "10" Option "!SendCoreEvents?" "yes"

EndSection?

Noteable differences between this and the version 3 config are that you specify a Device, not a Port, otherwise you get an error. Also, !AlwaysCore? from v3 has been replaced with !SendCoreEvents?.

You must also add to the !ServerLayout? section, despite that X might say: "(II) XINPUT: Adding extended input device "TOUCHSCREEN" (type: Elographics Touch Screen)"

Section "!ServerLayout?" Identifier "Default Layout" Screen "Default Screen"

InputDevice? "Generic Keyboard"

...

InputDevice? "ELO touchscreen"

EndSection?

6. Suggested reading

****Manpage for XF86Config ****

**** http://www.elotouch.com/Support/linux.asp ****

**** http://www.microtouch.com/mthtml/05a1_drivers.htm ****

**** http://www.hof-berlin.de/tablet/tablet.html (Thanks to Christer Olofsson for sending me this URL) ****

****The manual shipped with your touch screen :-) ****