Problems attempting to setup a USB MIDI device (not host)

[shuaulme1]

My goal is to write a MIDI music instrument with the Jetson Orin Nano and plug it into a PC to connect it to a synth using MIDI signals.

the USB gadget is there, but it’s used by the L4T, presumably to allow the PC to see it when you want to connect it using the SDK manager for example.

How I can I prevent the l4t gadget from being setup?

ls /sys/kernel/config/usb_gadget/
l4t midi_gadget

I setup the midi_gadget using a script like so (called by a service)

#!/bin/bash

Check if the script is run as root

if [[ $EUID -ne 0 ]]; then
echo “This script must be run as root”
exit 1
fi

Load USB gadget modules

modprobe libcomposite

Remove any existing USB gadget (to prevent conflicts)

GADGET_PATH=“/sys/kernel/config/usb_gadget/midi_gadget”
if [ -d “$GADGET_PATH” ]; then
echo “Removing existing gadget…”
echo “” > “$GADGET_PATH/UDC” 2>/dev/null
rm -rf “$GADGET_PATH”
sleep 1
fi

Create a new gadget

mkdir -p “$GADGET_PATH”
cd “$GADGET_PATH”

Set USB device attributes

echo 0x1d6b > idVendor # Linux Foundation
echo 0x0104 > idProduct # Multifunction Composite Gadget

Set device description strings

mkdir -p strings/0x409
echo “001” > strings/0x409/serialnumber
echo “manufacturer” > strings/0x409/manufacturer
echo “aproduct” > strings/0x409/product

Create configuration

mkdir -p configs/c.1/strings/0x409
echo “Config 1: MIDI” > configs/c.1/strings/0x409/configuration
echo 250 > configs/c.1/MaxPower

Create MIDI function

mkdir -p functions/midi.usb0
echo “0” > functions/midi.usb0/in_jack_id
echo “1” > functions/midi.usb0/out_jack_id

Bind the configuration to the function

ln -s functions/midi.usb0 configs/c.1

Enable the USB gadget

UDC=$(ls /sys/class/udc | head -n 1)
if [ -z “$UDC” ]; then
echo “Error: No available UDC found!”
exit 1
fi

but I get this when I start the service:

Feb 06 20:18:33 hp-proto2a sudo[2282]: rm: cannot remove ‘/sys/kernel/config/usb_gadget/midi_gadget/bDeviceProtocol’: Operation not permitted

Feb 06 20:18:33 hp-proto2a sudo[2282]: rm: cannot remove ‘/sys/kernel/config/usb_gadget/midi_gadget/bDeviceSubClass’: Operation not permitted

Feb 06 20:18:33 hp-proto2a sudo[2282]: rm: cannot remove ‘/sys/kernel/config/usb_gadget/midi_gadget/bDeviceClass’: Operation not permitted

Feb 06 20:18:34 hp-proto2a sudo[2287]: mkdir: cannot create directory ‘functions/midi.usb0’: No such file or directory

Feb 06 20:18:34 hp-proto2a sudo[2277]: /usr/local/bin/setup_usb_midi.sh: line 62: functions/midi.usb0/in_jack_id: No such file or directory

Feb 06 20:18:34 hp-proto2a sudo[2277]: /usr/local/bin/setup_usb_midi.sh: line 63: functions/midi.usb0/out_jack_id: No such file or directory

Feb 06 20:18:34 hp-proto2a sudo[2289]: ln: failed to create symbolic link ‘configs/c.1/midi.usb0’: No such file or directory

Feb 06 20:18:34 hp-proto2a sudo[2277]: /usr/local/bin/setup_usb_midi.sh: line 75: echo: write error: Invalid argument

Feb 06 20:18:34 hp-proto2a sudo[2277]: USB MIDI gadget setup complete.

Feb 06 20:18:34 hp-proto2a sudo[2276]: pam_unix(sudo:session): session closed for user root

which I’m wondering if it’s due to the fact that there is already a gadget in place.

any suggestions?

[DaneLLL]

Hi,
Please try to remove the service and see if your use-case works:

/opt/nvidia/l4t-usb-device-mode/nv-l4t-usb-device-mode.service

[shuaulme1]

Thank you DaneLLL, that worked for removing the l4t gadget. My problem now is that I need to add midi support in the kernel for my gadget to work.