This section lists common problems and possible solutions. If you experience other problems or would like to add a solution for a problem feel free to open an issue in our Github project or send us an email to

Permission denied when accessing the USB-SD-Mux

Problem: When using the control software a PermissionError: Permission denied is raised.

In the following example a user tries to access the sg-device without the appropriate permissions:

chris@dauntless:~$ usbsdmux /dev/sg0 get
Traceback (most recent call last):
  File "/tmp/usbsdmux/venv/bin/usbsdmux", line 10, in <module>
  File "/tmp/usbsdmux/…/usbsdmux/", line 77, in main
  File "/tmp/usbsdmux/…/usbsdmux/", line 55, in get_mode
  File "/tmp/usbsdmux/…/usbsdmux/", line 73, in read_register
  File "/tmp/usbsdmux/…/usbsdmux/", line 425, in write_read_to
  File "/tmp/usbsdmux/…/usbsdmux/", line 337, in _call_IOCTL
PermissionError: [Errno 13] Permission denied: '/dev/sg0'

The user has no sufficient permissions to access the device node for /dev/sg0.

To fix this issue either run the tool as root (e.g. using sudo) or use udev to grant access to the device to your user. The see Chapter Using as non-root user for setup instructions.

Access to the SD card fails with timeouts or read errors

Problem: Using the USB-SD-Mux introduces an additional load and additional disturbances for the micro SD card of your DUT. This can lead to problems like read errors and timeouts.

There are multiple workarounds for this issue:

  1. Many users have reported that using a slow micro SD card yields better results than using a fast micro SD card.

  2. Sometimes only ROM-Code (or integrated firmware) has trouble using the micro SD card inside the USB-SD-Mux. If this is the case, depending on your use-case, you may be able to load your bootloader from another media (like NAND-Flash or an eMMC) and afterwards access the SD card from inside this bootloader.

  3. Depending on your setup you are maybe able to change drive-stength or the output-impedance matching of the used pins. This can help to access the micro SD card inside the USB-SD-Mux.

  4. Depending on your setup you may be able to reduce the maximum clock frequency used.