This is a text-only version of the following page on https://raymii.org: --- Title : Run MS Teams on a coffee machine?!? (Or: Embedded Linux Framebuffer VNC client) Author : Remy van Elst Date : 08-04-2021 URL : https://raymii.org/s/blog/MS_Teams_on_a_Coffee_Machine_or_Framebuffer_VNC_Client.html Format : Markdown/HTML --- To fill some time [during compiling](https://xkcd.com/303/) I tried to get a VNC client running on a coffee machine, specifically to show MS Teams. At work I develop software for these coffee machines in C++, which allows me to do such fun stuff, because from a software point of view, it's just an ARM PC running linux with a framebuffer for graphics. I compiled a few framebuffer VNC clients, fired up an SSH tunnel and used `x11vnc` to share one specific window and after a few attempts, Teams was up and running on my 'new' second monitor. This post contains my little adventure in framebuffer VNC clients, but it's not a comprehensive guide as most of my other articles. Showing you how to set up an Openembedded server with a VariScite specific toolchain is way too much work to cross-compile a simple C program, but since that's my day job, why not use it for fun. It contains some tips for `x11vnc` and shows you two different framebuffer VNC clients, `fbvnc` and `directvnc`. ![teams on nio][1] > Microsoft Teams running on a coffee machine?!?

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**Important disclaimer: this was a fun side project, neither acknowledged nor endorsed by my employer. Their coffee machines can not run custom software under normal circumstances.** The instructions in this post are applicable to any linux framebuffer device. It could be a raspberry pi or even your own machine. Here is another picture with a keyboard attached, input works with fbvnc. The mouse is optional since the touchscreen works as well in fbvnc. I did not test user input (mouse/keyboard) much more, because I intended to use the device as a view only screen. Also, my spare board has a broken touch controller/screen, which is why I can re-use it as a second screen, otherwise it would be thrown out. ![teams5][20] For local development, I sometimes do it the reverse way around, run the coffee machine UI on my [local machine][8]. Manual testing is a rare occurrence, since by far a large part of our codebase is covered by unit tests and there is an extensive HTTP API. But still, sometimes there is a need for local testing, we have stubs, can run the QT UI locally and even [the flash UI][9] still runs with some hoops. And of course a bunch of coffee machines to test with, but who likes walking and manually pressing buttons if you can automate that stuff away? This is one of the Frankenstein just-enough-coffee-machines that serves as a second screen: ![teams 3][19] ### Second screen? So why not get an actual second screen? Well, I personally use just one screen, because I try to do one thing at a time. That one thing usually requires all of my focus and attention, so a second screen with all kinds of distractions doesn't really work for me. However, infrequently, I miss a second screen. During chat sessions or video call's where you're pair programming or to have a datasheet open. In such cases I would like a small screen which is easy to turn off when it's not needed anymore. A friend of mine is a video editor and he has a separate 5" screen, for use with Final Cut. That thing was expensive (due to colour correctness) and on AliExpress I could only find [these things, still expensive][6]. Then it occurred, our coffee machines all have 7" touch screens, they run linux and I have a bunch of Frankenstein just-enough-coffee-machines on my desk for testing. Why not use such a screen for the occasional chat window? The machines run either `gnash` with a flash UI, a `qt` UI or a [headless UI for touchless][10], which uses MQTT and an internal HTTP API. The QT ui also uses the HTTP API, flash still runs a custom communication protocol. Both QT and Gnash run on the framebuffer, there is no X server, so a regular VNC client will not work. Or the actual teams binary for that matter. ### x11vnc one window and a reverse SSH port forward I use the following command to start a VNC server on `localhost` only (because it runs without a password, `fbvnc` does not support that). The special thing is that that command allows me to pick one window which is shared over VNC, not the entire desktop or a screen region. x11vnc -id pick -viewonly -forever -localhost -geometry 800x600 -scale 800x600 -noxdamage The `-geometry` and `-scale` parameters are given because the machine screen has that resolution. It looks less weird that way. Since the VNC server is only accessible via localhost, I use SSH to setup a secure tunnel to the coffee machine and forward my machine's VNC port to the coffee machine: ssh -R 5900:127.0.0.1:5900 user@IP.OF.COFFEE.MACHINE **The coffee machines normally do not have SSH running or exposed. For local development we can turn it on, but it involves a signed package and UART.** Now, as far as the coffee machine is concerned, it has a port on `localhost:5900` which is also a working VNC `display:0`. Great! Let's continue on to VNC clients. Both VNC clients for the framebuffer were cross-compiled with out specific toolchain, instructions for that are not really applicable elsewhere. On a raspberry pi or other ARM board, you can just install `gcc` (`apt install build-essential`) and follow along. ### directvnc The first client I found was [directvnc][11]. Over 9 years old, seemingly dead, but I could find an [openembedded][12] [recipe][13] for it which worked right away, so that was easy. Too easy it appeared, because it works partly. As you can see on the image below, [one half of the screen was black][3] and the colours are a bit off on the other (working) half: ![teams 2][2] I [filed a github issue][14] but I don't expect it will be fixed, since the project seems dead. The curious thing was that other code using `directfb` did work on the entire screen, no issues [running the examples][3]. `directvnc` used `directfb` for the framebuffer rendering. I tried all the possible options in `/etc/directfbrc` and took a quick look at the code, but didn't find anything to make it work. And since it's a side project in my spare time, I decided to move on to the next client I found, `fbvnc`. If you're compiling yourself, you can clone the repository (`git clone https://github.com/drinkmilk/directvnc`) and run `autoreconf -vfi` then `automake`, then `./configure` and finish off with `make`. There should be a new binary in that folder. Make sure you have [directfb][16] installed as well, it's a dependency. On Debian (and Raspbian) you can install `directvnc` [as a package][17], no compilation required: apt install directvnc ### fbvnc `fbvnc` is a smaller, more bare-bones tool. The old Debian [webpages are of course offline][5], but archive.org still has copies. However, to my surprise, the [git repository has recent commits][7] from its author, [Ali Gholami Rudi - his homepage][18]! A `git clone` and `make fbvnc` in my cross-compile setup later I have a working binary. The connection failed at first, because I had password protected it. After removing the password, it worked right away. Way easier compilation setup (no `autotools`) and no dependency on `directfb`, saves a lot of work. `fbvnc` hard codes the host `127.0.0.1` and the port `5900`, but you can specify others on the command line: fbvnc hostname port There is no help or instructions, just a `connection failed` or `init failed`. The source is small and readable so figuring out what happens when is easy. After you start it, `CTRL+C` to quit doesn't work, to stop it you must stop `x11vnc`. Here is a screenshot of my entire KDE desktop running (scaled_ on the coffee machine, via VNC: ![kde][15] #### How does teams run? Performance wise, it's better then I expected. A tad bit laggy, but usable and even for video calls, not that much stuttering. Since it's all running on my workstation and only the rendering is on the coffee machine, I didn't expect any less. If I have some more spare time, I'll try to make a video sometime showing the performance. For an occasional second screen, it's just perfect. [1]: /s/inc/img/teams2.jpg [2]: /s/inc/img/teams1.jpg [3]: /s/inc/img/directvnc.png [4]: /s/inc/img/directfb-win.png [5]: http://web.archive.org/web/20130430135501/http://pocketworkstation.org/fbvnc.html [6]: https://web.archive.org/web/20210408180724/https://nl.aliexpress.com/item/1005002189869923.html?spm=a2g0o.cart.0.0.6cce3c00rwdBLC&mp=1 [7]: https://repo.or.cz/w/fbvnc.git [8]: /s/inc/img/gnash1.png [9]: /s/tags/gnash.html [10]: https://archive.md/uQJXv [11]: http://drinkmilk.github.com/directvnc/ [12]: http://git.toradex.com/cgit/meta-toradex-demos.git/tree/recipes-graphics/vnc/directvnc_0.7.8.bb?h=master [13]: https://archive.md/lBgET [14]: https://github.com/drinkmilk/directvnc/issues/1#issuecomment-815604974 [15]: /s/inc/img/fbvnc.png [16]: https://github.com/DirectFB/directfb [17]: https://web.archive.org/web/20210408185358/https://packages.debian.org/sid/directvnc [18]: http://litcave.rudi.ir [19]: /s/inc/img/teams3.jpg [20]: /s/inc/img/teams5.png --- License: All the text on this website is free as in freedom unless stated otherwise. 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