How to map a touchscreen#

With our Weston display compositor, you will need to explicitly configure which display the touchscreen should belong to.

For SimpleCore™ images, the main configuration file is /etc/touchscreens.json.

It is a key-value map that is probed in the following order

  • <ID_VENDOR_ID>:<ID_MODEL_ID>:<ID_SERIAL>

  • <ID_VENDOR_ID>:<ID_MODEL_ID>:<ID_PATH_TAG>

  • <ID_VENDOR_ID>:<ID_MODEL_ID>

if found the value of that key is the display name.

Available display names can be found with

$ cat /run/simplecore-weston.ini | grep -C 2 "output" | grep "name" | cut -d'=' -f2

An example#

Let’s say your USB input device is announced as /dev/input/event1. Now you can get all the needed attributes by running

$ udevadm info -n /dev/input/event1
P: /devices/platform/soc@0/32f10108.usb/38200000.dwc3/xhci-hcd.2.auto/usb3/3-1/3-1.2/3-1.2.3/3-1.2.3:1.0/0003:222A:0001.0001/input/input1/event1
N: input/event1
L: 0
S: input/touchscreen0
S: input/by-path/platform-xhci-hcd.2.auto-usb-0:1.2.3:1.0-event
S: input/by-id/usb-ILITEK_ILITEK-TP-event-if00
E: DEVPATH=/devices/platform/soc@0/32f10108.usb/38200000.dwc3/xhci-hcd.2.auto/usb3/3-1/3-1.2/3-1.2.3/3-1.2.3:1.0/0003:222A:0001.0001/input/input1/event1
E: DEVNAME=/dev/input/event1
E: MAJOR=13
E: MINOR=65
E: SUBSYSTEM=input
E: USEC_INITIALIZED=8071563
E: ID_INPUT=1
E: ID_INPUT_TOUCHSCREEN=1
E: ID_INPUT_WIDTH_MM=215
E: ID_INPUT_HEIGHT_MM=135
E: ID_VENDOR=ILITEK
E: ID_VENDOR_ENC=ILITEK
E: ID_VENDOR_ID=222a
E: ID_MODEL=ILITEK-TP
E: ID_MODEL_ENC=ILITEK-TP
E: ID_MODEL_ID=0001
E: ID_REVISION=0000
E: ID_SERIAL=ILITEK_ILITEK-TP
E: ID_TYPE=hid
E: ID_BUS=usb
E: ID_USB_INTERFACES=:030000:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=usbhid
E: ID_PATH=platform-xhci-hcd.2.auto-usb-0:1.2.3:1.0
E: ID_PATH_TAG=platform-xhci-hcd_2_auto-usb-0_1_2_3_1_0
E: LIBINPUT_DEVICE_GROUP=3/222a/1:usb-xhci-hcd.2.auto-1.2
E: DEVLINKS=/dev/input/touchscreen0 /dev/input/by-path/platform-xhci-hcd.2.auto-usb-0:1.2.3:1.0-event /dev/input/by-id/usb-ILITEK_ILITEK-TP-event-if00

In case you can describe the device uniquely with the help of <ID_VENDOR_ID> an <ID_MODEL_ID> (or you only have a single touchscreen of the corresponding manufacturer), add

"222a:0001": "<DISPLAY_NAME>"

to the configuration file (/etc/touchscreens.json).

In case you have multiple touchscreens of the same manufacturer (and ID_SERIAL is not a per-device value), add the values suffixed with the USB port they are connected to (ID_PATH_TAG)

"222a:0001:platform-xhci-hcd_2_auto-usb-0_1_2_3_1_0": "<DISPLAY_NAME_1>",
"222a:0001:platform-xhci-hcd_2_auto-usb-0_1_2_4_1_0": "<DISPLAY_NAME_2>",

Only static connection schemes are supported

This will not work if the USB port is set dynamically. Only static connections are possible.

If, for instance, we have two touchscreens of

  • <ID_VENDOR_ID>=1111 and <ID_MODEL_ID>=0001, connected to display LVDS-1

  • as well as <ID_VENDOR_ID>=2222 and <ID_MODEL_ID>=0001, connected to HDMI-1

the resulting configuration looks like

Automatic fallback

If the configured display isn’t available Weston will automatically fall back to the first display (usually LVDS, if available)

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