DESK-MX6UL-L/Peripherals/USB OTG

History
Version	Issue Date	Notes
1.0.0	Apr 2021	First DESK release
3.0.0	Mar 2022	DESK 3.0.0 release

Peripheral USB OTG

The USB OTG ports can be configured as Host or Device mode depending on the device tree configuration. In OTG mode they can be easily tested using the Mass Storage Gadget, which lets the device export a file as a mass storage device to the connected PC.

The USB OTG peripheral is not available - as default option - on AXEL ULite EVK. Please contact Sales department for this option. This peripheral is available on the i.MX6UL standard product SBCLynx

Device tree configuration

Here below an example of device tree configuration used on standard DAVE's kit for the AXEL ULite SOM where USB OTG1 is configured as otg while the USB OTG2 port is configured in host mode:

From imx6ul-lynx-som0013-cb002f.dts:

		pinctrl_usb_otg2: usbotg2grp {
			fsl,pins = <
				MX6UL_PAD_ENET2_TX_DATA1__GPIO2_IO12    0x17059 /* OTG2_PWR */
				MX6UL_PAD_ENET2_TX_EN__USB_OTG2_OC       0x17059 /* OTG2_OC */
			>;
		};
	};
};

and from imx6ul-lynx-som0013.dtsi:

		pinctrl_usb_otg2: usbotg2grp {
			fsl,pins = <
				MX6UL_PAD_ENET2_TX_DATA1__GPIO2_IO12    0x17059 /* OTG2_PWR */
				MX6UL_PAD_ENET2_TX_EN__USB_OTG2_OC       0x17059 /* OTG2_OC */
			>;
		};

		pinctrl_usb_otg2_1: usbotg2grp-1 {
			fsl,pins = <
				MX6UL_PAD_UART3_CTS_B__GPIO1_IO26	0x17059 /* OTG2_PWR */
				MX6UL_PAD_UART3_RTS_B__GPIO1_IO27	0x17059 /* OTG2_OC */
			>;
		};

Accessing the peripheral

Linux messages at boot time

...
...
[    3.691938] usb usb2: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 5.10
[    3.700663] usb usb2: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[    3.708200] usb usb2: Product: EHCI Host Controller
[    3.713101] usb usb2: Manufacturer: Linux 5.10.35-desk-mx6ul-l-3.0.0+g48931d32962e ehci_hcd
[    3.721517] usb usb2: SerialNumber: ci_hdrc.1
...
...

Usage in Host mode

When a USB peripheral is inserted, in the following example a memory mass storage device, the kernel recognizes the device (i.e. class, vendor id, product id, etc.)

[   86.792011] usb 1-1: new high-speed USB device number 3 using ci_hdrc
[   86.994587] usb 1-1: New USB device found, idVendor=0781, idProduct=5591, bcdDevice= 1.00
[   87.003001] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[   87.010294] usb 1-1: Product:  SanDisk 3.2Gen1
[   87.021695] usb 1-1: Manufacturer:  USB
[   87.028329] usb 1-1: SerialNumber: 03017128082020175157
[   87.044709] usb-storage 1-1:1.0: USB Mass Storage device detected
[   87.065893] scsi host0: usb-storage 1-1:1.0
[   88.094462] scsi 0:0:0:0: Direct-Access      USB      SanDisk 3.2Gen1 1.00 PQ: 0 ANSI: 6
[   88.114699] sd 0:0:0:0: [sda] 30031872 512-byte logical blocks: (15.4 GB/14.3 GiB)
[   88.138282] sd 0:0:0:0: [sda] Write Protect is off
[   88.153463] sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[   88.228657]  sda: sda1
[   88.248736] sd 0:0:0:0: [sda] Attached SCSI removable disk
[   90.031956] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)

Usage with mass-storage

root@desk-mx6ul-lynx:~# dd if=/dev/zero of=mass_storage count=32 bs=1M                                                                                                                                             
32+0 records in
32+0 records out
33554432 bytes (34 MB, 32 MiB) copied, 0.593427 s, 56.5 MB/s
root@desk-mx6ul-lynx:~# mkfs.msdos mass_storage
mkfs.fat 4.2 (2021-01-31)
root@desk-mx6ul-lynx:~# mkdir loop
root@desk-mx6ul-lynx:~# mount -o loop mass_storage loop
txtt@desk-mx6ul-lynx:~# echo "Test USB OTG with mass storage device" > loop/usb.txt
root@desk-mx6ul-lynx:~# umount loop/

then insert the g_mass_storage kernel module driver enabling an Windows PC to see it as a removable device

root@desk-mx6ul-lynx:~# modprobe g_mass_storage removable=y file=mass_storage
root@desk-mx6ul-lynx:~# dmesg | tail -n 7
[  205.107477] Mass Storage Function, version: 2009/09/11
[  205.107514] LUN: removable file: (no medium)
[  205.107758] LUN: removable file: /home/root/mass_storage
[  205.107775] Number of LUNs=1
[  205.113207] g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
[  205.113238] g_mass_storage gadget: userspace failed to provide iSerialNumber
[  205.113253] g_mass_storage gadget: g_mass_storage ready

Once the USB cable is connected to the PC, the storage is mounted and the usb.txt file is available:

$ cat /media/tomzy/42D5-CBA5/usb.txt 
Test USB OTG with mass storage device

The Windows PC also activate the driver and the disk is available as a Drive Unit (with the usb.txt file available).

Additional information

More information about Mass Storage Gadget driver is given in the kernel tree under Documentation/usb/mass-storage.rst

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