[alsa-devel] Hercules P32 DJ: severe sound distortion during MIDI transfers

[Guido Trentalancia]

Hello again Clemens.

> Il 22 marzo 2019 alle 15.06 Clemens Ladisch <clemens at ladisch.de> ha scritto:
> 
> 
> Guido Trentalancia wrote:
> > Also, the hardware is the same: Hercules P32 DJ (with exactly the same
> > firmware version 1.46 which is the latest).
> 
> Are the USB controllers the same (2.0/3.x, OHCI/UHCI/EHCI/xHCI)?
> 
> You wrote that "amidi -p hw:2,0,0 -d" causes the problem.  As long as no
> MIDI messages are actually received, the kernel or driver cannot affect
> what happens on the USB bus; the polling is done entirely by the host
> controller.

I have double-checked this too and I can now confirm: "amidi -p hw:2,0,0 -d" does not increase the RX/TX (I/O) bytes count in /proc/asound/card2/midi0.

So, what kind of operation does amidi trigger in the kernel which causes the problem ? What does it actually do ?

I saw you wrote the ALSA USB MIDI driver (sound/usb/midi.c). But the MIDI seems to run fine, I can receive (RX) data from the controller fine.

It is the audio part (card.c, pcm.c, clock.c and so on) that is being disturbed by simultaneous MIDI operation !

What do you say ?

> Regards,
> Clemens