Troubleshooting

Logging

FTDI uses the pyftdi logger.

It emits log messages with raw payload bytes at DEBUG level, and data loss at ERROR level.

Common error messages

“Error: No backend available”

libusb native library cannot be loaded. Try helping the dynamic loader:

  • On Linux: export LD_LIBRARY_PATH=<path>

    where <path> is the directory containing the libusb-1.*.so library file

  • On macOS: export DYLD_LIBRARY_PATH=.../lib

    where <path> is the directory containing the libusb-1.*.dylib library file

“Error: Access denied (insufficient permissions)”

The system may already be using the device.

  • On macOS: starting with 10.9 “Mavericks”, macOS ships with a native FTDI kernel extension that preempts access to the FTDI device.

    Up to 10.13 “High Sierra”, this driver can be unloaded this way:

    sudo kextunload [-v] -bundle com.apple.driver.AppleUSBFTDI
    

    You may want to use an alias or a tiny script such as pyftdi/bin/uphy.sh

    Please note that the system automatically reloads the driver, so it may be useful to move the kernel extension so that the system never loads it.

    Warning

    From macOS 10.14 “Mojave”, the Apple kernel extension peacefully co-exists with libusb and PyFtdi, so you no longer need - and should not attempt - to unload the kernel extension. If you still experience this error, please verify you have not installed another driver from FTDI, such as FTDI’s D2XX.

  • On Linux: it may indicate a missing or invalid udev configuration. See the Installation section.

  • This error message may also be triggered whenever the communication port is already in use.

“Error: The device has no langid”

  • On Linux, it usually comes from the same installation issue as the Access denied error: the current user is not granted the permissions to access the FTDI device, therefore pyusb cannot read the FTDI registers. Check out the Installation section.

“Bus error / Access violation”

PyFtdi does not use any native library, but relies on PyUSB and libusb. The latter uses native code that may trigger OS error. Some early development versions of libusb, for example 1.0.22-b…, have been reported to trigger such issues. Please ensure you use a stable/final versions of libusb if you experience this kind of fatal error.

“serial.serialutil.SerialException: Unable to open USB port”

May be caused by a conflict with the FTDI virtual COM port (VCOM). Try uninstalling the driver. On macOS, refer to this FTDI macOS guide.

Slow initialisation on OS X El Capitan

It may take several seconds to open or enumerate FTDI devices.

If you run libusb <= v1.0.20, be sure to read the Libusb issue on macOS with OS X 10.11+.

Reporting a bug

Please do not contact the author by email.

Fill in an issue on GitHub.