After some poking around i confirmed that the usbhid driver was working - and also default enabled in FreeBSD15 kernel. Xev tool printed the correct keycode events

keycode 122 = XF86AudioLowerVolume 
keycode 123 = XF86AudioRaiseVolume 
keycode 172 = XF86AudioPlay

The problem narrowed down to how to map these event to something useful

I found a working solution in this discussion thread, by using the x11/sxhkd daemon to pass the events to mixer(8)

https://forums.freebsd.org/threads/howto-enabling-multimedia-keys-gamepads-joysticks-for-desktop-usbhid.84464/

I had to tweak the sxhkd config a bit to work properly with mixer

~/.config/sxhkd/sxhkdrc

XF86Audio{Play,LowerVolume,RaiseVolume}         
         mixer {vol.mute="toggle",vol="-3%", vol="+3%"}

Then I invoke the sxhkd daemon from my ~/.xsession file

sxhkd &
exec /usr/local/bin/fvwm3

Viola!

#FreeBSD #Solved #X11 #FVWM3 #Xorg #AskFedi