Suppose you have the really odd idea that you have some primitive computer device with a keyboard that outputs data via a serial communications line, and you want to route that to an Xorg keyboard input device. Actually, this isn’t that bad of an idea, old fashioned barcode readers and smart scales used this trick before the advent of USB and Bluetooth. Well, here’s the long story short of the easy way to do this.
inputattach --baud 2400 --sunkbd /dev/ttyUSB0
There are a variety of different devices supported through different drivers, if you have a matching such device (unlikely), then pick that one. Otherwise, simply pick whichever device you can find the best documentation on for the protocol and develop your peripheral to support that. Sun keyboard, Sun mouse, and Microsoft mouse are all pretty well documented.
Now, here is the lowdown of my twisted search. In the end, beyond merely being able to find information on the Internet, some lateral thinking was required to make things work out.
20191103/DuckDuckGo linux use a serial port input as a keyboard
20191103/DuckDuckGo linux use a serial port input as a gui keyboard
20191103/DuckDuckGo linux serial keyboard driver
20191103/https://wiki.archlinux.org/index.php/Serial_input_device_to_kernel_input
20191103/DuckDuckGo xorg serial port keyboard
20191103/https://askubuntu.com/questions/288324/how-to-forward-serial-devices-input-to-x
20191103/https://help.ubuntu.com/community/BarcodeReaders
20191103/https://launchpad.net/serial-text
20191103/DuckDuckGo xorg serial keyboard
20191103/DuckDuckGo xorg keyboard ttyUSB0
20191103/DuckDuckGo xorg keyboard ttyS0
20191103/https://help.ubuntu.com/community/SerialMouseHowto
Ah, yes, here it is! Specifications on the communication protocol of Sun serial keyboards. Yeah, it wasn’t exactly what I was looking for, I was looking for a really dumb keyboard driver that could support RS-232 ASCII data directly and translate it into keyboard input events, but on second thought, the Sun keyboard protocol is pretty simple and it isn’t that bad to write my own Sun keyboard driver wrapper on the Apple II side. Plus, it would make for more features than I was originally envisioning.
20191104/DuckDuckGo stowaway serial keyboard
20191104/https://sourceforge.net/directory/?q=serial%20to%20keyboard
20191104/DuckDuckGo barcode reader inputattach keyboard
This is an interesting though not very informative read.
20191104/http://lkml.iu.edu/hypermail/linux/kernel/0612.3/0400.html
20191104/DuckDuckGo ps/2 keyboard over rs-232
20191104/https://en.wikipedia.org/wiki/PS/2_port
This is a great information source.
20191104/DuckDuckGo sun serial keyboard
20191104/http://kentie.net/article/sunkbd/
20191104/http://kentie.net/article/sunkbd/page2.htm
20191104/http://kentie.net/article/sunkbd/KBD.pdf
As for other serial keyboard protocols… well, a cursory web search seems to point that some of the less popular ones are naturally no very well documented. That being said, I’d favor the more popular ones over the less popular ones for simply that reason.
20191104/DuckDuckGo dec serial keyboard
Information on creating an adapter for an Apple Newton keyboard.
20191104/DuckDuckGo newton serial keyboard
http://jimandnoreen.com/?p=259
20191104/DuckDuckGo microsoft serial mouse protocol
20191104/https://www.kryslix.com/nsfaq/Q.12.html
20191104/DuckDuckGo sun serial mouse protocol
20191104/https://linux.die.net/man/4/mouse
In regard to Raspberry Pi projects, attaching a serial keyboard has some significant benefits, namely that it makes it easier to develop and test your own computer keyboards. Hooray!