Setup the USB device mode

katim · May 27, 2026, 4:58am

Hi, I’m trying to set up the Rubik Pi in USB device mode. I need to connect two Rubik Pi boards via a USB cable. For this, one device must act as a “USB device” and the other as a “USB host.”

According to the official documentation, USB device mode can only be configured on the USB 2.0 Type-A port and the USB 3.0 Type-C port. Among these, the Type-C port can automatically switch between host and device modes. To avoid conflicts, I used a USB Type-C to Type-A cable and connected the 2.0 Type-A port configured as “USB device”, to the Type-C port configured as “USB host” on the two Rubik Pi boards.

However, nothing appears in sudo dmesg -w.

I also tried setting up the Rubik Pi in USB device mode with a mobile phone and a PC, but even in those setups, the Rubik Pi could not be detected by those devices.

kinkin · May 27, 2026, 6:30am

Could you please share the specific test commands and steps you used?

katim · May 28, 2026, 4:54am

Hi,
thanks for repying,

Here in first setup i use, USB type-C to type-A cable. Type-C goes to “HOST” config rubic and Type-A goes to “DEVICE” config rubic.

Configurations “DEVICE” side


root@tnn-service:/sys/kernel/config/usb_gadget# modprobe -r g_ether

root@tnn-service:/sys/kernel/config/usb_gadget# mkdir g1

root@tnn-service:/sys/kernel/config/usb_gadget# l

**g1**/

root@tnn-service:/sys/kernel/config/usb_gadget# cd g1/

root@tnn-service:/sys/kernel/config/usb_gadget/g1# ls
UDC bDeviceProtocol bMaxPacketSize0 bcdUSB **functions** idVendor **os_desc** **webusb**
bDeviceClass bDeviceSubClass bcdDevice **configs** idProduct max_speed **strings**

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo 0x1d6b > idVendor
echo 0x0104 > idProduct

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkdir strings/0x409

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo "1234567890" > strings/0x409/serialnumber
echo "Rubic" > strings/0x409/manufacturer
echo "MassStorage" > strings/0x409/product

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkdir configs/c.1/strings/0x409
mkdir: cannot create directory ‘configs/c.1/strings/0x409’: No such file or directory

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkdir configs/c.1

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkdir configs/c.1/strings/0x409

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo "Config 1" > configs/c.1/strings/0x409/configuration

root@tnn-service:/sys/kernel/config/usb_gadget/g1# 

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkdir functions/mass_storage.0

root@tnn-service:/sys/kernel/config/usb_gadget/g1# dd if=/dev/zero of=/tmp/test.iso bs=1M count=2048
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB, 2.0 GiB) copied, 1.87076 s, 1.1 GB/s
root@tnn-service:/sys/kernel/config/usb_gadget/g1# mkfs.ext4 /tmp/test.iso
mke2fs 1.47.0 (5-Feb-2023)
Discarding device blocks: done                            
Creating filesystem with 524288 4k blocks and 131072 inodes
Filesystem UUID: ef27c07b-5365-4a17-afe7-58e4a11b23bd
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done 

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo "/tmp/test.iso" > functions/mass_storage.0/lun.0/file

root@tnn-service:/sys/kernel/config/usb_gadget/g1# ln -s functions/mass_storage.0/ configs/c.1/f3

root@tnn-service:/sys/kernel/config/usb_gadget/g1# mount -t debugfs none /sys/kernel/debug/
mount: /sys/kernel/debug: none already mounted or mount point busy.
       dmesg(1) may have more information after failed mount system call.

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo "" > /sys/kernel/debug/usb/8c00000.usb/mode

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo "device" > /sys/kernel/debug/usb/8c00000.usb/mode

root@tnn-service:/sys/kernel/config/usb_gadget/g1# cat UDC

root@tnn-service:/sys/kernel/config/usb_gadget/g1# echo 8c00000.usb > UDC

root@tnn-service:/sys/kernel/config/usb_gadget/g1# cat /sys/kernel/debug/usb/8c00000.usb/mode
device

Configurations “HOST” side. Since we are using type C

root@rubikpi-0316:/home/ubuntu# cat /sys/kernel/debug/usb/a600000.usb/mode
device

root@rubikpi-0316:/home/ubuntu# echo "host" > /sys/kernel/debug/usb/a600000.usb/mode

root@rubikpi-0316:/home/ubuntu# cat /sys/kernel/debug/usb/a600000.usb/mode
host

Connect the USB cable and observer “sudo dmesg -w”

on “HOST” side

[ 1565.295508] xhci-hcd xhci-hcd.4.auto: xHCI Host Controller
[ 1565.295548] xhci-hcd xhci-hcd.4.auto: new USB bus registered, assigned bus number 4
[ 1565.297714] xhci-hcd xhci-hcd.4.auto: hcc params 0x0230fe65 hci version 0x110 quirks 0x0000008000000010
[ 1565.297788] xhci-hcd xhci-hcd.4.auto: irq 193, io mem 0x0a600000
[ 1565.297975] xhci-hcd xhci-hcd.4.auto: xHCI Host Controller
[ 1565.297994] xhci-hcd xhci-hcd.4.auto: new USB bus registered, assigned bus number 5
[ 1565.298013] xhci-hcd xhci-hcd.4.auto: Host supports USB 3.0 SuperSpeed
[ 1565.298399] usb usb4: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 6.08
[ 1565.298413] usb usb4: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[ 1565.298421] usb usb4: Product: xHCI Host Controller
[ 1565.298442] usb usb4: Manufacturer: Linux 6.8.0-1057-qcom xhci-hcd
[ 1565.298451] usb usb4: SerialNumber: xhci-hcd.4.auto
[ 1565.299159] hub 4-0:1.0: USB hub found
[ 1565.299209] hub 4-0:1.0: 1 port detected
[ 1565.299676] usb usb5: We don't know the algorithms for LPM for this host, disabling LPM.
[ 1565.299800] usb usb5: New USB device found, idVendor=1d6b, idProduct=0003, bcdDevice= 6.08
[ 1565.299811] usb usb5: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[ 1565.299836] usb usb5: Product: xHCI Host Controller
[ 1565.299843] usb usb5: Manufacturer: Linux 6.8.0-1057-qcom xhci-hcd
[ 1565.299849] usb usb5: SerialNumber: xhci-hcd.4.auto
[ 1565.300617] hub 5-0:1.0: USB hub found
[ 1565.300684] hub 5-0:1.0: 1 port detected
[ 1565.536097] usb 4-1: new full-speed USB device number 2 using xhci-hcd
[ 1575.750464] xhci-hcd xhci-hcd.4.auto: xHCI host not responding to stop endpoint command
[ 1575.770639] xhci-hcd xhci-hcd.4.auto: xHCI host controller not responding, assume dead
[ 1575.778775] xhci-hcd xhci-hcd.4.auto: HC died; cleaning up
[ 1575.784534] usb usb4-port1: couldn't allocate usb_device

on “DEVICE” side
nothing on dmesg logs.

check the “HOST” side lsusb

root@rubikpi-0316:/home/ubuntu# lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 002: ID 0b95:1790 ASIX Electronics Corp. AX88179 Gigabit Ethernet
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
root@rubikpi-0316:/home/ubuntu# cat /sys/kernel/debug/usb/a600000.usb/mode
host

kinkin · May 28, 2026, 11:03am

We are currently syncing this issue internally.