DESK-MX6UL-L/Peripherals/USB OTG

History
Version	Issue Date	Notes
1.0.0	Apr 2021	First DESK 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.

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.dtsi:

&usbotg1 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_usb_otg1_id>;
        vbus-supply = <&reg_usb_otg1_vbus>;
        dr_mode = "otg";
        srp-disable;
        hnp-disable;
        adp-disable;
        status = "disabled";
};

&usbotg2 {
        vbus-supply = <&reg_usb_otg2_vbus>;
        dr_mode = "host";
        status = "disabled";
};
...
...
&iomuxc {
...
...
	pinctrl_usb_otg1_id: usbotg1idgrp {
		fsl,pins = <
			MX6UL_PAD_GPIO1_IO00__ANATOP_OTG1_ID    0x17059
		>;
	};

	pinctrl_usb_otg1: usbotg1grp {
		fsl,pins = <
			MX6UL_PAD_ENET2_RX_DATA0__GPIO2_IO08    0x10b0 /* OTG1 PWR */
			MX6UL_PAD_ENET2_RX_DATA1__GPIO2_IO09    0x17059 /* OTG1_OC */
		>;
	};

	pinctrl_usb_otg1_oc: usbotg1grp1 {
		fsl,pins = <
			MX6UL_PAD_ENET2_RX_DATA0__GPIO2_IO08    0x10b0 /* OTG1 PWR */
			MX6UL_PAD_ENET2_RX_DATA1__USB_OTG1_OC   0x17059 /* OTG1_OC */
		>;
	};

	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 */
		>;
	};

From imx6ul-lynx-som0013-cb002f.dts:

&reg_usb_otg1_vbus {
        pinctrl-0 = <&pinctrl_usb_otg1_oc>;
};

&usbotg1 {
        over-current-active-low;
        status = "okay";
};

&usbotg2 {
        over-current-active-low;
        status = "okay";
};

...
...
&iomuxc {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_hog_gpios>;

        imx6ul-lynx {
...
...
                pinctrl_usb_otg1: usbotg1grp {
                        fsl,pins = <
                                MX6UL_PAD_ENET2_RX_DATA0__GPIO2_IO08    0x10b0 /* OTG1 PWR */
                                MX6UL_PAD_ENET2_RX_DATA1__USB_OTG1_OC   0x17059 /* OTG1_OC */
                        >;
                };

                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 */
                        >;
                };

Accessing the peripheral

Linux messages at boot time

...
...
[    3.387128] usb_otg1_vbus: supplied by SWBST
[    3.418986] usb_otg2_vbus: supplied by SWBST
[    5.245408] usb_otg1_vbus: disabling
...
...

Usage with mass-storage

root@imx6qdlxelk:~# dd if=/dev/zero of=mass_storage count=256 bs=1M
256+0 records in
256+0 records out
268435456 bytes (268 MB, 256 MiB) copied, 15.924 s, 16.9 MB/s
root@imx6qdlxelk:~# mkfs.msdos mass_storage
mkfs.fat 4.1 (2017-01-24)
root@imx6qdlxelk:~# mkdir loop
root@imx6qdlxelk:~# mount -o loop mass_storage loop
root@imx6qdlxelk:~# echo "Test USB OTG with mass storage device" > loop/usb.txt
root@imx6qdlxelk:~# umount loop

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

root@imx6qdlxelk:~# modprobe g_mass_storage removable=y file=mass_storage
[  891.807023] Mass Storage Function, version: 2009/09/11
[  891.813145] LUN: removable file: (no medium)
[  891.818901] LUN: removable file: /home/root/mass_storage
[  891.824754] Number of LUNs=1
[  891.827901] g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
[  891.834955] g_mass_storage gadget: userspace failed to provide iSerialNumber
[  891.842109] g_mass_storage gadget: g_mass_storage ready
root@imx6qdlxelk:~#

Once the USB cable is connected to the PC, the kernel prints the following messages:

root@imx6qdlxelk:~# [  892.036840] g_mass_storage gadget: high-speed config #1: Linux File-Backed Storage

and the Windows PC 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.txt

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