commit c572c572058e54ac64919015b112e9e2e5fc7a50
Author: wp <wp@noreply.localhost>
Date:   Tue Aug 5 22:01:38 2025 -0500

    Add README.md

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+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
+1. Load wireshark and start recording packets from the master USB bus (bus:0) just prior to connecting the printer
+2. Connect a Dymo 400 Twin Turbo printer to the system with USB
+3. Stop logging USB packets after a minute
+4. 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: [malformed]
+5. In terminal,  `lsusb -v -d 0922:0018`
+6. Notice the gibberish value in the iSerial field.
+7. 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 `b''`
+
+
+```python
+# 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''
+
+
+```
+
+References
+
+https://www.beyondlogic.org/usbnutshell/usb5.shtml#StringDescriptors