It appears the Dymo 400 Twin Turbo does not report the correct device serial number. This prevents us from using more than one of these devices on a system because the device URI is not properly formed.
This will possibly need a USB device quirk added to the Linux kernel.
An alternative is to possibly implement a fix in dymo-cups-drivers. However, I think the problem occurs higher up the software stack.
How to identify the problem
- Load wireshark and start recording packets from the master USB bus (bus:0) just prior to connecting the printer
- Connect a Dymo 400 Twin Turbo printer to the system with USB
- Stop logging USB packets after a minute
- Review packet data and notice a packet received from the device has a malformed string
- The packet will be a GET DESCRIPTOR Response STRING with bLength: 30, bDescriptorType: 0x03 (String), and malformed bString:
〰㘀 ㌀ 㘀㔀㜀㔀
- In terminal,
lsusb -v -d 0922:0018 - Notice the gibberish value in the iSerial field.
- When setting up the printer, notice the device URI is
usb://DYMO/LabelWriter%20Twin%20Turbo?serial=??????????????
The problem occurs because the default format for USB device descriptor STRINGs is uint-16-le. However, the Dymo-TT includes an extra byte at the start of the data returned from the device.
For example, the serial bString from a Dymo 450 is received as b'\x31\x00\x37\x00\x31\x00\x30\x00\x30\x00\x36\x00\x31\x00\x36\x00\x31\x00\x38\x00\x34\x00\x32\x00\x33\x00\x30\x00'.
However, an example from the Dymo-TT is b'\x30\x30\x00\x36\x00\x31\x00\x30\x00\x33\x00\x30\x00\x31\x00\x30\x00\x31\x00\x36\x00\x31\x00\x35\x00\x37\x00\x35'.
Decoding the Dymo 450 string using uint-16-le yields "17100616184230", whereas the Dymo-TT string yields gibberish values.
The physical labels found on the Dymo 450 include "1740021750110" and another "1750110". The physical labels on the Dymo-TT are "93085-2053234" and "06440293085". It seems the digital "serial" numbers don't match the physical serial numbers marked. However, the digital serial ID is still unique for each device.
A second Dymo-TT connected previously reports 〰㘀 㠀\xe3\x84\x80㈀\xe3\x84\x80㐀㐀㔀㔀㌀㔀㤀 as the device SerialNumber as recorded in the kernel log. It's unknown what the actual binary value should be from this.
# from pyUSB
import usb.core
import usb.util
vid = 0x0922 # Dymo VID
pid450 = 0x0020 # Dymo 450 PID
pidtt = 0x0018 # Dymo Twin Turbo PID
dymo450 = usb.core.find(idVendor=vid, idProduct=pid450)
dymott = usb.core.find(idVendor=vid, idProduct=pidtt)
print(f"Dymo 450 Serial: {dymo450.serial_number}") # yields 17100616184230
print(f"Dymo-Twin-Turbo Serial: {dymott.serial_number}") # yields gibberish
print(f"Dymo 450 Raw Serial value: {usb.control.get_descriptor(dymo450,254,0x03,dymo450.iSerialNumber,dymo450.langids[0])[2:30].tobytes().decode('utf-16-le')}") # returns 17100616184230
print(f"Dymo-TT Raw Serial value: {usb.control.get_descriptor(dymott,254,0x03,dymott.iSerialNumber,dymott.langids[0])[2:30].tobytes().decode('utf-16-le')}") # returns gibberish
print(f"Dymo 450 string result as bytes: {usb.control.get_descriptor(dymo450,254,0x03,dymo450.iSerialNumber,dymo450.langids[0])[2:30].tobytes().decode('utf-16-le').encode('utf-8')}") # returns b'17100616184230'
print(f"Dymo 450 string result as bytes: {usb.control.get_descriptor(dymott,254,0x03,dymott.iSerialNumber,dymott.langids[0])[2:30].tobytes().decode('utf-16-le').encode('utf-8')}") # returns b'\xe3\x80\xb0\xe3\x98\x80\xe3\x84\x80\xe3\x80\x80\xe3\x8c\x80\xe3\x80\x80\xe3\x84\x80\xe3\x80\x80\xe3\x84\x80\xe3\x98\x80\xe3\x84\x80\xe3\x94\x80\xe3\x9c\x80\xe3\x94\x80'
The Twin-Turbo serial is supposed to be 006103010161575. Due to the extra 0 byte b'\x30', the rest of the return data becomes shifted and is interpreted like
b'\x30\x30\x00\x36\x00\x31\x00\x30\x00\x33\x00\x30\x00\x31\x00\x30\x00\x31\x00\x36\x00\x31\x00\x35\x00\x37\x00\x35'.decode('utf-16-le') or literally unicode values \x3500\x3700\x3500\x3100\x3600\x3100\x3000\x3100\x3000\x3300\x3000\x3100\x3600\x3030
Note: Linux Mint 22.1 <- Ubuntu 24.04 Noble <- Debian Trixie/sid <- Kernel 6.8.0-71-generic; pyusb version 1.3.1; python version 3.12.3
References
https://www.beyondlogic.org/usbnutshell/usb5.shtml#StringDescriptors
https://github.com/pyusb/pyusb/issues/154
https://github.com/pyusb/pyusb/blob/master/usb/util.py#L320
https://github.com/torvalds/linux/blob/master/drivers/usb/core/quirks.c
https://docs.kernel.org/admin-guide/reporting-issues.html