MIDI handshake for Pioneer DJ DJM-250MK2 to enable recording LINE/PHONO channels

[Takashi Iwai]

On Mon, 18 Jan 2021 23:41:35 +0100,
František Kučera wrote:
> 
> Dne 25. 08. 20 v 17:36 František Kučera napsal(a):
> > 1) The direct (before fader) PHONO/LINE recording channels are silent until some (yet unknown) special command is send to the mixer. There is quite a lot communication over USB in both directions and I have to dig through the dumps. This would be a separate commit and I do not know, how long it could take.
> 
> As mentioned earlier, the Pioneer DJM devices are somehow broken and by default they produce only silence on LINE/PHONO recording channels.
> 
> It was really challenging but it is no more hopeless – in the meantime, someone described, how it works inside, and I wrote a standalone program called djm-fix that fixes the device and enables the LINE/PHONO channels (so the mixer is usable e.g. for DVS). Details are described here: <https://blog.frantovo.cz/c/387/>. The djm-fix tool is still a bit raw, but it works for me and at least one more DJM-250MK2 owner confirmed, that it works.
> 
> Is it possible to move this fix to the kernel level? Or should it stay rather as a standalone tool? I think that it would be nice to have Pioneer DJM devices fully working out of the box without additional tools.
> 
> The fix consists of a MIDI handshake – we need to send and receive some messages, compute some hash and then periodically send a keep-alive message (when we stop, the LINE/PHONO channels become silent again).

I haven't looked closely, but if it's about MIDI messaging, it can be
implemented in the kernel, too (only if it fits better than
user-space), yes.  If it's over HID, it's a different story, though.


Takashi