This article provides how to allow the USB2.0/USB3.0 device controller act as a serial port device 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 Gadget configfs : Device Drivers > USB support > USB Gadget Support. Select <M> for “USB Gadget functions configurable through configfs“. Select [*] for “Generic serial bulk in/out”, “Abstract Control Model (CDC ACM)“ or “Object Exchange Model (CDC OBEX)“.

Execute the make command to build the Linux image.

ConfigFS (CDC ACM)

Configure serial gadget through configfs saved as a file named setup_serial.

#!/bin/sh

USB2_ACM_EN=on
USB3_ACM_EN=on

KERNEL_PATH=/lib/modules/`uname -r`/kernel
GADGET_PATH=$KERNEL_PATH/drivers/usb/gadget
FUNCTION_PATH=$GADGET_PATH/function

COMPOSITE=$GADGET_PATH/libcomposite.ko
U_SERIAL=$FUNCTION_PATH/u_serial.ko

insmod $COMPOSITE
insmod $U_SERIAL

# disable debug message
echo 0 > /sys/module/sunplus_udc/parameters/dmsg

mkdir -p /sys/kernel/config
mount -t configfs none /sys/kernel/config

if [ $USB2_ACM_EN = on]
then
    cd /sys/kernel/config/usb_gadget

    # create gadget folder
    mkdir g1
    cd g1

    # setup gadget
    echo 64 > bMaxPacketSize0
    echo 0x200 > bcdUSB

    # composite class
    echo 0x02 > bDeviceClass

    mkdir -p configs/c.1
    mkdir -p configs/c.1/strings/0x409
    echo "USB2.0 Serial Console" > configs/c.1/strings/0x409/configuration

    mkdir strings/0x409
    echo "1234" > strings/0x409/serialnumber
    echo "Sunplus" > strings/0x409/manufacturer
    echo "SP7350" > strings/0x409/product

    mkdir functions/acm.gs0
    ln -s functions/acm.gs0 configs/c.1

    # bind UDC
    echo "f8102800.usb" > UDC
fi

if [ $USB3_ACM_EN = on]
then
    cd /sys/kernel/config/usb_gadget

    # create gadget folder
    if [ $USB2_ACM_EN = on]
    then
        mkdir g2
        cd g2
    else
        mkdir g1
        cd g1
    fi

    # setup gadget
    echo 64 > bMaxPacketSize0
    echo 0x300 > bcdUSB

    # composite class
    echo 0x02 > bDeviceClass
    
    mkdir -p configs/c.1
    mkdir -p configs/c.1/strings/0x409
    echo "USB3.0 Serial Console" > configs/c.1/strings/0x409/configuration
    
    mkdir strings/0x409
    echo "5678" > strings/0x409/serialnumber
    echo "Sunplus" > strings/0x409/manufacturer
    echo "SP7350" > strings/0x409/product
    
    mkdir functions/acm.gs1
    ln -s functions/acm.gs1 configs/c.1
    
    # bind UDC
    echo "f80a1000.dwc3" > UDC
fi

Test (CDC ACM) Configuartions

Use sh setup_serial command to configure USB 2.0 and USB3.0 device controllers as serial gadgets.

# sh setup_serial

ttyGS0 and ttyGS1 in /dev are represented for the USB2.0 serial gadget and the USB3.0 one.

After connecting the USB2.0 serial gadget and the USB3.0 one to a Windows PC with USB cables, “USB Serial Device (COM6)“ (USB2.0 serial gadget) and “USB Serial Device (COM7)“ (USB3.0 serial gadget) will show up in “Ports (COM & LPT)” in Device Manager. “Prolific UBS-to-Serial Comm Port (COM9)” is the default terminal (UART0) of the SP7350 platform.

Serial Device Test

Use the communication tool of Tera Term for the test with the Windows PC.

TX Test for USB2.0 Serial Gadget

Use the following command to transfer characters of “SP7350 USB2.0 Serial Gadget TX Test“ from ttyGS0 (USB2.0 serial gadget) to COM6.

# echo "SP7350 USB2.0 Serial Gadget TX Test" > /dev/ttyGS0

The characters will be received by COM6 open by Tera Term.

TX Test for USB3.0 Serial Gadget

Use the following command to transfer characters of “SP7350 USB3.0 Serial Gadget TX Test“ from ttyGS1 (USB3.0 serial gadget) to COM7.

# echo "SP7350 USB3.0 Serial Gadget TX Test" > /dev/ttyGS1

The characters will be received by COM7 open by Tera Term.

RX Test for USB2.0 Serial Gadget

Use the following command to be ready to receive characters transferred from COM6 through ttyGS0 (USB2.0 serial gadget).

# cat /dev/ttyGS0

Input the characters of “SP7350 USB2.0 Serial Gadget RX Test" in COM6 open by Tera Term and press “Enter”.

SP7350 USB2.0 Serial Gadget RX Test

The characters will be received by ttyGS0.

RX Test for USB3.0 Serial Gadget

Use the following command to be ready to receive characters transferred from COM7 through ttyGS1 (USB3.0 serial gadget).

# cat /dev/ttyGS1

Input the characters of “SP7350 USB3.0 Serial Gadget RX Test" in COM7 open by Tera Term and press “Enter”.

SP7350 USB3.0 Serial Gadget RX Test

The characters will be received by ttyGS1.

How to Implement an USB2.0 / USB3.0 Serial Gadget