When you are trying to configure touch screen on Linux machine, internet offers examples Xorg.conf configuration but without explanation were numbers in it came from. If you have different touch screen you might be out of luck or guess what to do. In this post, I will try to explain how to examine your device using evtest and try out settings using xinput without restarting X server or installing any drivers other than built-in evdev.
We have a couple of 3M MicroTouch M150 touch screens which are VGA monitors (1024*768 resolution) with USB touchscreen interface which is reported as:
dpavlin@t42:~$ lsusb -d 0596:0001 Bus 002 Device 002: ID 0596:0001 MicroTouch Systems, Inc. TouchscreenA bit of googling later, I found out that there are two different drivers for microtouch devices, but both of them support serial devices only. Not giving up that easily I decided to see what xinput reports about it (without any additional drivers installed!):
dpavlin@t42:~$ xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ 3M 3M USB Touchscreen - EX II id=9 [slave pointer (2)]
⎜ ↳ SynPS/2 Synaptics TouchPad id=11 [slave pointer (2)]
⎜ ↳ TPPS/2 IBM TrackPoint id=12 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Sleep Button id=8 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=10 [slave keyboard (3)]
↳ ThinkPad Extra Buttons id=13 [slave keyboard (3)]
This seems like a good news, but when I tried to use it, it seemed that cursor would move only in middle of screen (with X axis swapped) so I wasn't very happy about it. Examining properties of device in more detail revealed that it has property to swap axes and calibrate them, but what to write into those values?
dpavlin@t42:~$ xinput list-props 9
Device '3M 3M USB Touchscreen - EX II':
Device Enabled (139): 1
Coordinate Transformation Matrix (141): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
Device Accel Profile (263): 0
Device Accel Constant Deceleration (264): 1.000000
Device Accel Adaptive Deceleration (265): 1.000000
Device Accel Velocity Scaling (266): 10.000000
Device Product ID (257): 1430, 1
Device Node (258): "/dev/input/event7"
Evdev Axis Inversion (267): 0, 0
Evdev Axis Calibration (268): <no items>
Evdev Axes Swap (269): 0
Axis Labels (270): "Abs X" (261), "Abs Y" (262)
Button Labels (271): "Button Unknown" (260), "Button Unknown" (260), "Button Unknown" (260), "Button Wheel Up" (145), "Button Wheel Down" (146)
Evdev Middle Button Emulation (272): 0
Evdev Middle Button Timeout (273): 50
Evdev Third Button Emulation (274): 0
Evdev Third Button Emulation Timeout (275): 1000
Evdev Third Button Emulation Button (276): 3
Evdev Third Button Emulation Threshold (277): 20
Evdev Wheel Emulation (278): 0
Evdev Wheel Emulation Axes (279): 0, 0, 4, 5
Evdev Wheel Emulation Inertia (280): 10
Evdev Wheel Emulation Timeout (281): 200
Evdev Wheel Emulation Button (282): 4
Evdev Drag Lock Buttons (283): 0
First task was was to flip x axes to make it move left-right instead of right-left. This can be acomplised using following command:
dpavlin@t42:~$ xinput set-prop 9 267 1 0Parameters are device id, property id, X axis swap and Y axis swap. If you don't know how many parameters property takes, just put one, try it out and if it returns errors, keep adding parameters until it suceeds.
Next, I needed to calibrate screen to track my finger moving over surface. This is where evtest comes into play. It's low level utility which enables you to see input events before they are passwd to Xorg server. You will have to run it as root as follows:
dpavlin@t42:~$ sudo evtest
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0: AT Translated Set 2 keyboard
/dev/input/event1: Lid Switch
/dev/input/event2: Sleep Button
/dev/input/event3: Power Button
/dev/input/event4: ThinkPad Extra Buttons
/dev/input/event5: Video Bus
/dev/input/event6: PC Speaker
/dev/input/event7: 3M 3M USB Touchscreen - EX II
/dev/input/event8: SynPS/2 Synaptics TouchPad
/dev/input/event9: TPPS/2 IBM TrackPoint
Select the device event number [0-9]: 7
Input driver version is 1.0.1
Input device ID: bus 0x3 vendor 0x596 product 0x1 version 0x410
Input device name: "3M 3M USB Touchscreen - EX II"
Supported events:
Event type 0 (EV_SYN)
Event type 1 (EV_KEY)
Event code 330 (BTN_TOUCH)
Event type 3 (EV_ABS)
Event code 0 (ABS_X)
Value 7353
Min 0
Max 16384
Event code 1 (ABS_Y)
Value 4717
Min 0
Max 16384
Properties:
Testing ... (interrupt to exit)
Immidiatly we can see minimum and maximum values for both axes and putting figer on top-left corner of screen produced (a lot of) output like this:
Event: time 1386078786.506710, -------------- SYN_REPORT ------------ Event: time 1386078786.510712, type 3 (EV_ABS), code 0 (ABS_X), value 13919 Event: time 1386078786.510712, type 3 (EV_ABS), code 1 (ABS_Y), value 2782After a few touches I had coordinates which where something like this:
| 14046,2722 | 2380,2986 | |
| 7994,7819 | ||
| 13743,13616 | 2624,13545 | |
dpavlin@t42:~$ xinput set-prop 9 268 2380 14000 2800 13500Trying it out on screen proved that it now works as expected. Let's call this success and remember that current Xorg knows a lot of tricks itself (recognising USB touch devices is one of them).
As a side note you don't really need to use evtest to get device position. Using xinput list id syntax displays you more-or-less same information, including last point which you touched on device as seen below:
dpavlin@t42:~$ xinput list 9
3M 3M USB Touchscreen - EX II id=9 [slave pointer (2)]
Reporting 3 classes:
Class originated from: 9. Type: XIButtonClass
Buttons supported: 5
Button labels: "Button Unknown" "Button Unknown" "Button Unknown" "Button Wheel Up" "Button Wheel Down"
Button state:
Class originated from: 9. Type: XIValuatorClass
Detail for Valuator 0:
Label: Abs X
Range: 0.000000 - 16384.000000
Resolution: 0 units/m
Mode: absolute
Current value: 13889.000000
Class originated from: 9. Type: XIValuatorClass
Detail for Valuator 1:
Label: Abs Y
Range: 0.000000 - 16384.000000
Resolution: 0 units/m
Mode: absolute
Current value: 2832.000000
However evtest will run in loop until you stop it with Ctrl+C so I find it a little bit easier to use than re-running xinput list id.