Unloading FTDI drivers on a Mac for libftdi

Installing libftdi on a mac is easy these days.

123	$ /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" $ brew install libusb $ brew install libftdi

But then you write a program using libftdi, and surprise surprise, it won't let your program open the FTDI device. Something like:

FTDI USB open error: unable to claim usb device. Make sure the default FTDI driver is not in use (-t)

So we can check which FTDI kernel extensions are loaded using

kextstat | grep -i ftdi

, and if there are any, on a modern system, it'll be AppleUSBFTDI. It can be unloaded easily:

sudo kextunload -bundle-id com.apple.driver.AppleUSBFTDI

And if you're lucky, you can now run your programs against libftdi with no issue. When you're done, kextload replacing kextunload in the command above re-loads the driver.

However, you may face a seemingly impossible problem: you unload the kext, you try to run your program, and you get the same exact error. Unplugging and replugging the device doesn't help. It clearly enumerates - it's visible when you do

system_profiler SPUSBDataType

- yet you can't take it!

If this happens, try running

kextstat | grep -i ftdi

again; you'll likely see that the legacy FTDI driver - com.FTDI.driver.FTDIUSBSerialDriver - is now present! Once you unload this too, re-run your code, and it should be able to talk to the FTDI device.

Note: Originally written 11/4/2015, updated 5/4/2021 to note Homebrew's new installer.

Ches Koblents