Maximum number of MIDI USB devices

[taskovskig]

Hi there,

Yesterday I acquired Rasp Pi 3, installed Raspbian, and started my long lusted midi sequencer project. At the end of the day, I need to connect 11 USB MIDI devices using powered MIDI hubs. Note that I have done this on regular PC using Ubuntu. No problems there. When I try to replicate my setup from Ubuntu to Raspbian, it turns out that I can not connect more than 7 external devices (total of eight including the stock 'Midi Through Port-0'). Each new MIDI USB device is recognized, but the dmesg output is:

[ 681.974078] snd-usb-audio 1-1.4.3:1.0: cannot find the slot for index -1 (range 0-7), error: -19
[ 681.974103] usb 1-1.4.3: cannot create card instance 7
[ 681.974480] snd-usb-audio 1-1.4.3:1.1: cannot find the slot for index -1 (range 0-7), error: -19
[ 681.974502] usb 1-1.4.3: cannot create card instance 7

no matter the 9-th device I connect. Any useful info regarding this issue will be highly appreciated.

Thanks in advance

[taskovskig]

It seems that new kernel will solve the problem. Default Raspbian kernel conf has this line:

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# CONFIG_SND_DYNAMIC_MINORS is not set

Just follow the instructions for kernel building here:
https://www.raspberrypi.org/documentati ... iguring.md
https://www.raspberrypi.org/documentati ... uilding.md
During the configuration, make sure to have this 2 lines in .config (or via menuconfig)

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CONFIG_SND_DYNAMIC_MINORS=y
CONFIG_SND_MAX_CARDS=16

After booting to the new kernel, the maximum number of USB sound devices that can be connected is 15 (there's one default MIDI Through port). You can check this by:

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$ sudo modprobe snd-usb-audio
$ cat /sys/module/snd_usb_audio/parameters/index
-2,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1

Previously, with the old kernel it was:

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$ cat /sys/module/snd_usb_audio/parameters/index
-2,-1,-1,-1,-1,-1,-1,-1

I've built the new kernel, and the Pi3 successfully booted. I'll post the results tonight.

[AndyBorek]

You saved my life. I could not understand the reason why my n-th midi device is not recognized (where n > 7). Based on your description I successfully rebuilt the kernel and increased the number of cards to 32(!!!) just in case my inventory grows due to severe GAS.

These devices are happily connected at the same time:

• Novation Circuit
• AKAI APC 40
• 2 x Roland UM3G 3IN/3OUT USB Midi Hub
• 1 x Roland UM1 1IN/1OUT USB Midi
• Modal CraftSynth
• Modal CraftRhythm
• Novation LaunchControl XL
• Digidesign MBox

Added a midi.conf to /etc/modprobe.d/

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##############################x
# Midi alsa configurations

options snd-seq-dummy ports=32

This one creates 32 Midi Through Port in Alsa. I'll use that as a kind of IAC emulation to create internal Midi buses for future Mididings manipulation.

[taskovskig]

Glad you managed to solve your problem. Cheers.