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OS X Device Drivers
For correct device operation with yad2xx the FTDI supplied D2XX device driver must be installed and be configured to 'match' against the USB device. This topic can be a little confusing due to there being multiple vendors offering FTDI device drivers, i.e. FTDI and Apple. OS X version is also a factor, as are the USB devices vendor and product identifiers (VID/PID).
The following device drivers are available:
- Apple Serial Driver
- FTDI Serial Driver (aka VCP Driver)
- FTDI D2XX Driver
Every USB device is allocated a unique vendor id/product id combo. When a device is attached OS X uses the VID/PID to determine which device driver to use.
USB device vendors such as FTDI pay a licence fee and are allocated a unique number. For FTDI this unique vendor id (VID) is 0x0403. All devices manufactured by FTDI will come with this value set.
Product identifiers (PIDs), are allocated by the individual manufacturers. Because the PID is an unsigned 16-bit number there are a possible 65536 values available. FTDI sell multiple kinds of USB devices, the assigned PID varies according to the device. Common values are [1]:
| Device | Default VID/PID |
|---|---|
| FT232BM/L/Q, FT245BM/L/Q | 0x0403, 0x6001 |
| FT232RL/Q, FT245RL/Q | 0x0403, 0x6001 |
| FT2232C/D/L | 0x0403, 0x6010 |
| FT2232HL/Q | 0x0403, 0x6010 |
| FT4232HL/Q | 0x0403, 0x6011 |
| FT232HL/Q | 0x0403, 0x6014 |
On OS X you can view the VID/PID settings for every attached USB device in the System Report (Apple Menu -> About This Mac).
When a new USB device is attached OS X interrogates the device, a process known as USB device enumeration [2]. The information obtained is used to locate the corrected device driver for the device.
For OS X releases 10.9+ (Mavericks and above), Apple provide their own device driver. It is configured to match against all default FTDI VID/PID combinations (see above table). Devices matched by this driver operate as serial ports and are located in the filesystem under /dev/cu.usbserial-xxxxx. Devices configured this way can be operated using the POSIX communications API [3].
Devices using the Apple driver cannot be operated using yad2xx. If you try to connect to one of these devices it will report already being open. You can disable the Apple Driver using the following command: sudo kextunload –b com.apple.driver.AppleUSBFTDI
Be warned, this disables the Apple driver for all FTDI devices using default VID/PID.
For reference, the Apple driver is located in: /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBFTDI.kext
FTDI supply their own serial driver for OS X. Its use is optional and you must manually install it. It installs into (v2.3+): /Library/Extensions/FTDIUSBSerialDriver.kext
Like the Apple driver, its matches all default FTDI VID/PID devices. It also is configured to match many 3rd party devices based on an FTDI chip. The list of supported devices is too long to list here, see: /Library/Extensions/FTDIUSBSerialDriver.kext/Contents/Info.plist
The FTDI serial driver will not cause conflicts with the Apple driver. In all instances where the device could match either driver the FTDI serial driver is used.
Because the FTDI serial driver is signed it cannot be modified. Editing the driver files, for example Info.plist, will prevent OS X from loading the driver (editing changes the package signature). This means that the FTDI serial driver can only be used with devices known to FTDI. It cannot be used with custom VID/PID devices.
Like the Apple driver, devices should be programmed using the POSIX communications API. You can disable the FTDI Serial driver using: sudo kextunload –b com.FTDI.driver.FTDIUSBSerialDriver
The FTDI D2XX Driver is an optional installation. It allows the device to be used as a serial port. It also allows access to more advanced device modes such as bit bang, JTAG, I2C, SPI etc.
Devices may experience driver clashes. This is based on the device VID/PID combo and the installed drivers. The default FTDI VID/PID settings will match the Apple driver (always) and the FTDI Serial driver (if installed). In either case the driver must be unloaded before the D2XX driver will work.
It is possible to reprogram an FTDI devices VID/PID [1]. Changing to a VID/PID combo outside those configured for the Apple driver means the Apple driver will not match. Changing to a value outside those configured for the FTDI Serial driver means that driver will not match.
Devices that fail to match the Apple and FTDI Serial driver can only use the D2XX driver.
##References
- FTDI - Technical Note TN100 - USB Vendor ID / Product ID Guidelines
- FTDI - Technical Note TN113 - Simplified Description of USB Device Enumeration
- Apple Developer Notes - Working With a Serial Device