I have a basic HP 100 wired keyboard. This keyboard has 3 extra keys - Sound Mute, Volume Down, Volume Up buttons. It is autodetected and configured in Devuan, Ubuntu distros which I have in this desktop. But, in FreeBSD-13.0, not even xev is detecting these keys. Any idea how to configure this keyboard sound buttons?
Nop, the HP 100 keyboard (a.k.a. HSA-A001K) volume keys do not display with the showkey application (tested from outside X11).
Basically, in FreeBSD an X server obtains its input from the kbdmux(4) device, which speaks the atkbd(4) protocol. There are no keycodes in that protocol for those keys.
To get those keys into the X server, it would have to talk to uhid(4) or ugen(4) devices; which out of the box it doesn't. Instead you have to run uhidd(8) and configure mappings from the USB HID usages to atkbd(4) codes in uhidd.conf(5) that are higher numbered than the standard ones.
uhidd(8) basically speaks the uhid(4) protocol to a USB HID keyboard and creates extra fake vkbd(4) devices whose inputs get fanned in to kbdmux(4) as if you had a bunch of extra PS/2 keyboards that could make these extra keycodes.
