I'm using Milkytracker 0.90.85, on Arch Linux with Deltafire's PKGBUILD, modified to add --with-jack, and using JACK 0.118.0. Everything I post is done with Jack running in the background, with a working setup for MilkyTracker and my keyboard doing it's midi in, and output through my laptop's speakers.
The issue I have is when I start Milkytracker with Jack as the default sound driver, I get the following output:
ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave
ALSA: Failed to open device 'default' (Device or resource busy)
JACK: Mixer frequency: 48000
JACK: Latency = 1024 frames
cannot lock down memory for RT thread (Cannot allocate memory)
[arin@eee ~]$ milkytracker
JACK: Mixer frequency: 48000
JACK: Latency = 1024 frames
RtMidiIn::openPort: error starting MIDI input thread!
RtMidiIn::openPort: error starting MIDI input thread!
I would've just left it there, if I didn't manage to trick MilkyTracker by starting it up with ALSA as the sound driver, which gives the following:
ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave
ALSA: Failed to open device 'default' (Device or resource busy)
And then changing the driver to Jack, which add this to the output:
JACK: Mixer frequency: 48000
JACK: Latency = 1024 frames
cannot lock down memory for RT thread (Cannot allocate memory)
Thus allowing me to add notes with my midi keyboard when I set it's input to 129:RtMidi Input Client, which in turn points to 0:Midi Through Port-0 in my qjackctl "Connections" window (see diagram attached to post).
I think I was rather thorough, but if there's any links I happen to have left out, I'll fill them in.