USB MIDI Devices problem

Windows
1

Hi,

I design a standalone JUCE application, which processes some MIDI data coming from MIDI Devices and send it to another MIDI Devices. I’ve got a problem with some of MIDI Devices which are connected via USB - my keyboard KETRON SD9, and poor quality USB to MIDI interface.

The whole system requires DAW app for work. When I run e.g. Cubase (the same also on Cakewalk and Ableton), and create the MIDI track with some data, then I set the MIDI outputs of this track to this USB MIDI devices. When I run my app and I want to select the same USB-MIDI devices as I set in DAW, my app goes to crash. Moreover, when I do something similar with MIDI Input in my app - so I choose the USB-MIDI input first on DAW, and then the same in my app, everything works correctly. But when I want to disable this MIDI Device in my app, it also goes to crash.

I perform the debugging of my app. I have seen that my app crashes when the functions: startBackgroundThread(), stopBackgroundThread() and isBackgroungThreadRunning are recalled. Of course I cannot abandon this, because my app will not send out any MIDI data. In the second case (with MIDI IN) my app crashes when the function MidiDevice->stop() is recalled. When I was writing the MIDI I/O services, I based on MidiDemo.h project.

Last but not least - I’ve got an audio interface Focusrite Scarlett 6i6 2nd Gen. I use its MIDI input and output, and I can freely enable / disable the Focusrite USB MIDI device on DAW and my app, and it works correctly all the time.
What should I do? Maybe I do something wrong? Where is the problem - in my app, in drivers for this USB-MIDI device, or something more?

Thanks in advance :wink:

P.S. This USB-MIDI devices works ONLY on Windows. It doesn’t work on Mac.

2

Under Windows, the class compliant midi driver does not support more than on app opening the same midi port. The manufacturer can supply a driver which is written in a way that allows more than one application to open the same midi port. Having said that, I wouldn’t expect attempting that would cause a crash, but instead a failure when opening the port.

1 Like
3

I try to implement an “reaction” on wrongly opened MIDI device, but it doesn’t solve the problem. My app operates and send MIDI data as midi buffers, and I need to run the BackgroundThread - which causes a crash. Only my app crashes, any DAW doesn’t crash.
I will write about this problem in user manual, and also write to driver developers to inform they about this issues.