This document demonstrates how to implement an USB 2.0 / USB 3.0 mass storage gadget on SP7350 platforms.

Table of Contents

Kernel Setup

Enter the kernel configuration by running the following command in the top directory of project.

# make kconfig

Select submenus for USB 2.0 controller : Device Drivers > USB support > USB Gadget Support > USB Peripheral Controller. Select <*> for “Sunplus USB 2.0 Device Controller“.

Select submenus for USB 3.0 controller : Device Drivers > USB support. Select <*> for “DesignWare USB3 DRD Core Support“ and select “Dual Role mode“ for “Deware USB3 DRD Core Support“.

Select submenus for USB OTG Transceive driver : Device Drivers > USB support > USB Physical Layer drivers. Select <*> for “Sunplus USB OTG Transceive driver“.

Select submenus for USB Gadget configfs : Device Drivers > USB support > USB Gadget Support. Select <M> for “USB Gadget functions configurable through configfs“ and [*] for “Mass storage“.

Execute the make command to build the Linux image.

Create a backing storage file

The backing storage file must be prepared before the gadget uses it.

Use the following command to create a 32MB file (backing_file) filled with zeros.

# dd bs=1M count=32 if=/dev/zero of=/backing_file
32+0 records in
32+0 records out
33554432 bytes (34 MB, 32 MiB) copied, 0.0850515 s, 395 MB/s

Use the following command to create the FAT file system in backing_file.

# mkfs.fat /backing_file
mkfs.fat 4.1 (2017-01-24)

ConfigFS

Configure mass storage gadget through configfs saved as a file named usb_mass_storage. UDC_NAME is “f8102800.usb” for USB 2.0 Controller. UDC_NAME is “f80a1000.dwc3” for USB 3.0 Controller.

#!/bin/bash

MODULES=/lib/modules/`uname -r`/kernel

LIBCOMPOSITE=/$MODULES/drivers/usb/gadget/libcomposite.ko
FUNCTION=/$MODULES/drivers/usb/gadget/function/usb_f_mass_storage.ko

BACKING_FILE=/backing_file
UDC_NAME="f8102800.usb"
# UDC_NAME="f80a1000.dwc3"

#install the drivers
insmod $LIBCOMPOSITE
insmod $FUNCTION

#mount configfs
mount -t configfs none /sys/kernel/config

#create gadget
mkdir /sys/kernel/config/usb_gadget/g1
cd /sys/kernel/config/usb_gadget/g1
echo "64" > bMaxPacketSize0
echo "0x200" > bcdUSB

#create configuration
mkdir configs/c.1
mkdir configs/c.1/strings/0x409
echo 120 > configs/c.1/MaxPower

#create functions
mkdir functions/mass_storage.usb0
echo "$BACKING_FILE" > functions/mass_storage.usb0/lun.0/file

#link functions and configuration
ln -s functions/mass_storage.usb0 configs/c.1

#activate
echo $UDC_NAME > UDC

Implementation

After updating the image to the SP7350 platform, booting the system and copying the backing_file to it, use sh usb_mass_storage command to configure UDC (USB 2.0 or USB 3.0) as a mass storage gadget.

After connecting the mass storage gadget to a Windows PC through an USB cable, “E:\” will show up in “Portable Devices” of “Device Manager” and “Linux File-Stor Gadget USB Device“ in “Disk drivers“.

How to Implement an USB 2.0 / USB 3.0 Mass Storage Gadget on SP7350 Platforms

Kernel Setup

Create a backing storage file

ConfigFS

Implementation