Advanced Usage

libftdi function access

Three attributes of Device instances are documented which allow direct access to the underlying libftdi functionality.

1. fdll - this is a reference to the loaded libftdi library, loaded via ctypes. This should be used with the normal ctypes protocols.

2. ctx - this is a reference to the context of the current device context. It is managed as a raw ctypes byte-string, so can be modified if required at the byte-level using appropriate ctypes methods.

3. ftdi_fn - a convenience function wrapper, this is the preferred method for accessing library functions for a specific device instance. This is a function forwarder to the local fdll attribute, but also wraps the device context and passes it as the first argument. In this way, using device.ftdi_fn.ft_xyz is more like the D2XX driver provided by FTDI, in which the device context is passed in at initialisation time and then the client no longer needs to care about it. A call to:

   >>> device.ftdi_fn.ft_xyz(1, 2, 3)
   

   is equivalent to the following:

   >>> device.fdll.ft_xyz(ctypes.byref(device.ctx), 1, 2, 3)
   

   but has the advantages of being shorter and not requiring ctypes to be in scope.

   incorrect operations using any of these attributes of devices are liable to crash the Python interpreter

Examples

The following example shows opening a device in serial mode, switching temporarily to bit-bang mode, then back to serial and writing a string. Why this would be wanted is anyone’s guess ;-)

>>> from pylibftdi import Device
>>>
>>> with Device() as dev:
>>>    dev.ftdi_fn.ftdi_set_bitmode(1, 0x01)
>>>    dev.write('\x00\x01\x00')
>>>    dev.ftdi_fn.ftdi_set_bitmode(0, 0x00)
>>>    dev.write('Hello World!!!')

The libftdi documentation should be consulted in conjunction with the ctypes reference for guidance on using these features.

Selecting the underlying libftdi library

Since pylibftdi 0.12, the Driver exposes libftdi_version() and libusb_version() methods, which return a tuple whose first three entries correspond to major, minor, and micro versions of the libftdi driver being used.

Note there are two major versions of libftdi - libftdi1 can coexist with the earlier 0.x versions - it is now possible to select which library to load when instantiating the Driver. Note on at least Ubuntu Linux, the libftdi1 OS package actually refers to libftdi 0.20 (or similar), whereas libftdi1-2 refers to the more recent 1.x release (currently 1.5):

Python 3.10.6 (main, May 29 2023, 11:10:38) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from pylibftdi import Driver
>>> Driver().libftdi_version()
libftdi_version(major=1, minor=5, micro=0, version_str='1.5', snapshot_str='unknown')
>>> Driver("ftdi1").libftdi_version()
libftdi_version(major=1, minor=5, micro=0, version_str='1.5', snapshot_str='unknown')
>>> Driver("ftdi").libftdi_version()
libftdi_version(major=0, minor=0, micro=0, version_str='< 1.0 - no ftdi_get_library_version()', snapshot_str='unknown')

If both are installed, pylibftdi prefers libftdi1 (e.g. libftdi 1.5) over libftdi (e.g. 0.20). Since different OSs require different parameters to be given to find a library, the default search list given to ctypes.util.find_library is defined by the Driver._lib_search attribute, and this may be updated as appropriate. By default it is as follows:

_lib_search = {
    "libftdi": ["ftdi1", "libftdi1", "ftdi", "libftdi"],
    "libusb": ["usb-1.0", "libusb-1.0"],
}

This covers Windows (which requires the ‘lib’ prefix), Linux (which requires its absence), and Mac OS X, which is happy with either.