LVGL x wscons(4) x Lua on OpenBSD

This integrates LVGL, MQTT, Lua, and OpenBSD to provide a platform for building touch screen interfaces.

This implements LVGL drivers for the OpenBSD wsdisplay(4) or drm(4) frame buffer devices, and wsmouse(4) devices as a pointer. The program connects to an MQTT server, and provides integration between MQTT and LVGL via Lua.

But why?

I have a long term plan to get something like a Sonoff NSPanel Pro or a Tuya T6E based board running OpenBSD instead of the crippled and likely to be an abandonware version of Android that they ship with. wslv would be the basis for the user interface they provide.

Alternatively, a cheap mini PC and a touch screen mounted on the wall would also work.

While LVGL and wscons provide the user interface, MQTT allows it to interact with other hardware or visa versa. Lua provides a relatively easy scripting language to build an interface out of LVGL.

While it is possible to run a desktop environment and browser in kiosk mode to provide a user interface, integrating with the OpenBSD wscons devices directly allows for precise control of the supported peripherals. It should also be portable to resource constrained systems that are not able to support a full browser environment.

Also, I'm an idiot and make up work for myself.

Todo

• Learn LVGL

How?

• Install OpenBSD on supported hardware

Anything that provides a framebuffer and a mouse/touchscreen should be Good Enough(tm).

• Install Lua 5.3, libspng, and git via pkg_add

• Get the source code

git clone and an update of the submodules is probably the easiest way

• Run make obj and then make

• Run ./obj/wslv on the console.

wslv needs permission to open the display and input devices. By default it tries to open /dev/ttyC0 or /dev/dri/card0 for the display, and /dev/wsmouse0 for a pointer. When you log in on the console the system changes the ownership of these devices so you can use them as a non-privileged user.

Usage

wslv requires an MQTT server and a Lua script. These can be specified with the -h and -l command line options respectively.

The full set of command line options are:

• -4

Force wslv to use IPv4 for the MQTT server connection.

• -6

Force wslv to use IPv6 for the MQTT server connection.

• -d devname

Use devname as the name of the device in MQTT topics. By default wslv uses the short host name of the local system.

• -h mqtthost

The host name for the MQTT server.

• -i idletime

The number of seconds of idle time before the screen will blank. By default the idle time is 2 minutes.

• -l script.lua

The Lua script used to control LVGL on the display.

• -M wsmouse

A wsmouse(4) device to use as a LVGL pointer. If no pointers are specified wslv will use /dev/wsmouse0 by default. Multiple pointers may be specified.

• -p mqttport

The MQTT server port to connect to. wslv will default to port 1883.

• -W wsdisplay

The wsdisplay(4) device to use as the LVGL display. wslv will default to /dev/ttyC0. If the display appears to support DRM and Kernel Mode Setting, wslv will close the wsdisplay(4) device and try opening /dev/dri/card0 instead.

• -r

Display a Reload button on the screen that triggers a reload of the Lua script used to control the interface.

MQTT

The MQTT messages that wslv sends and receives are inspired by Tasmota and OpenHASP.

wslv uses tele/DEVNAME/LWT as the topic for "Last Will and Testament" messages. Once connected it publishes Online. If it's disconnected the MQTT server should publish Offline.

The state of the screen is published as part of tele/DEVNAME/STATUS. The screen can be manually controlled by sending ON (or 1), OFF (or 0), or TOGGLE (or 2) to cmnd/DEVNAME/screen.

Lua scripts can use wslv.tele(topic, payload) to publish messages. The topic argument to the wslv.tele() method is added to the end of tele/DEVNAME/ before being sent. ie, wslv.tele('foo', 'bar') will send bar to tele/DEVNAME/foo.

MQTT messages sent to topics starting with cmnd/DEVNAME/ will be given to the Lua script to handle if it provides a cmnd(topic, payload) function for wslv to call. The cmnd/DEVNAME/ prefix is removed from the topic before the Lua cmnd() handler is called.

Lua scripts can also publish or subscribe to any MQTT topic they want with wslv.publish() and wslv.subscribe() respectively. MQTT messages can be received by an mqtt_message() function in the Lua script.