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

[Be]

I discourage doing this in the kernel. If Pioneer did this in their drivers on Windows and macOS, I would recommend doing it in the kernel. But they do not; Rekordbox does it at the application level. Mixxx users are currently unable to use the phono inputs of these devices regardless of OS (see https://mixxx.discourse.group/t/pioneer-djm-250-mk2/17001/29 ). The best way to implement this would be through Mixxx's MIDI controller mapping system so that it works across Linux, Windows, and macOS.

I am CCing Olivia Mackintosh because the Pioneer DJM 750 likely uses the same or very similar MIDI signals. They could probably share one MIDI script in Mixxx. The Pioneer DJM 900 NXS2 probably uses the same or very similar signals too.

If you're interested in implementing this in Mixxx, let's continue the discussion in Mixxx's Zulip chat: https://mixxx.zulipchat.com/

> Dne 19. 01. 21 v 9:54 Takashi Iwai napsal(a):
> >/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. />
> Yes, it is only MIDI. The scenario is:
>
> 1) send a greeting message to the mixer
>
> 2) receive a greeting message
>
> 3) send another constant message
>
> 4) receive the response
>
> 5) compute something and send it back
>
> 6) receive the confirmation message
>
> 7) start sending a keep-alive message each 200 ms
>
> Specific received messages might be consumed by kernel (invisible for user-space), but others should flow undisturbed to the user-space. The sent messages should be injected and intermixed with normal messages coming from user-space. The kernel should not claim exclusive access to the MIDI device, because user-space tools might want to use it too.
> 
> Is there already anything similar, for inspiration?
>
> Franta


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