Non-root access for ST-LINK and USB-to-serial devices

Accessing the ST-LINK programming interfaces, USB-to-serial converters and some other USB devices from a non-root account requires the creation of dedicated udev rules to set access permissions.

Go straight to Final config or read on for details.

Step by step

When a USB device is plugged, executing lsusb should show it. For the ST-LINK interface of a STM32F3 Discovery board:

Bus 001 Device 008: ID 0483:3748 STMicroelectronics ST-LINK/V2

and the device /dev/bus/usb/001/080 will be created.

To give read and write access to non-root users the simplest way is to create a .rules file in /etc/udev/rules.d/ with a udev rule like this:

# STM32F3DISCOVERY rev A/B - ST-LINK/V2
ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", TAG+="uaccess"

This rule will give access for the logged user to the USB device with idVendor 0483 and idProduct 3748.

To be a little more restrictive let’s make sure that we offer read and write access only for the logged user and tie the rule to the USB subsystem:

# STM32F3DISCOVERY rev A/B - ST-LINK/V2
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="600", TAG+="uaccess"

Note: One can also add a group restriction like GROUP="plugdev" to permit the access only for the members of this group.

/dev/bus/usb/001/xxx is not a friendly name but we have the option to use a SYMLINK:

# STM32F3DISCOVERY rev A/B - ST-LINK/V2
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2_%n"

will also create an alias for the device, /dev/stlinkv2_8. Better but far from perfect.

The device number (8 for this example) will change with each plugging of the device. If the device have a unique field it can be used to create a clearly defined name. I have not found one for ST-LINK interfaces.

Read USB-to-serial converters for more information.

ST-LINK interfaces

The following script creates the access rules for ST-LINK V2, V2.1 and V3:

#!/bin/bash

sudo tee /etc/udev/rules.d/70-st-link.rules > /dev/null <<'EOF'
# ST-LINK V2
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2_%n"

# ST-LINK V2.1
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374b", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2-1_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3752", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2-1_%n"

# ST-LINK V3
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374d", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3loader_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374e", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374f", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3753", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
EOF

sudo udevadm control --reload-rules
sudo udevadm trigger

USB-to-serial converters

Some USB-to-serial converters have a serial field. If is unique it can be use to name those clearly.

Example for:

a generic USB-to-serial convertor with CP2102 USB to UART bridge programmed with serial 0099
a generic USB-to-serial convertor with CP2102 USB to UART bridge programmed with serial 0100
ESP32-DevKitC with CP2102 USB to UART bridge programmed with serial 0101

we can make the following rules:

# the blue USB-to-serial adapter
SUBSYSTEMS=="usb", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", ATTRS{serial}=="0099", MODE="600", TAG+="uaccess", SYMLINK+="u2s-blue"
# the black USB-to-serial adapter
SUBSYSTEMS=="usb", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", ATTRS{serial}=="0099", MODE="600", TAG+="uaccess", SYMLINK+="u2s-black"
# ESP32-DevKitC
SUBSYSTEMS=="usb", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", ATTRS{serial}=="0101", MODE="600", TAG+="uaccess", SYMLINK+="esp32-devkitc"

and the devices will be available also under the following aliases:

/dev/u2s-blue
/dev/us2-black
/dev/esp32_devkit

Almost perfect BUT those CP201x are all programmed from factory with serial number 0001 ! However those can be reprogrammed. I have not done it but if you need more information search for AN721 in Silicon Labs’s Technical Resource.

Final config

The following script creates access rules for ST-LINK V2, V2.1 and V3 and for some USB-to-serial converters:

#!/bin/bash

sudo tee /etc/udev/rules.d/70-st-link.rules > /dev/null <<'EOF'
# ST-LINK V2
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2_%n"

# ST-LINK V2.1
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374b", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2-1_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3752", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv2-1_%n"

# ST-LINK V3
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374d", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3loader_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374e", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="374f", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3753", MODE="600", TAG+="uaccess", SYMLINK+="stlinkv3_%n"
EOF

sudo tee /etc/udev/rules.d/70-usb-to-serial.rules > /dev/null <<'EOF'
# CP2101 - CP 2104
SUBSYSTEMS=="usb", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="600", TAG+="uaccess", SYMLINK+="usb2ser_%n"

# ATEN UC-232A
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0557", ATTRS{idProduct}=="2008", MODE="600", TAG+="uaccess", SYMLINK+="usb2ser_aten_%n"
EOF

sudo udevadm control --reload-rules
sudo udevadm trigger