"""
pylibftdi - python wrapper for libftdi
Copyright (c) 2010-2014 Ben Bass <benbass@codedstructure.net>
See LICENSE file for details and (absence of) warranty
pylibftdi: http://bitbucket.org/codedstructure/pylibftdi
"""
# The Bus descriptor class is probably useful outside of
# pylibftdi. It tries to be to Python what bitfields are
# to C. Its only requirement (which is fairly pylibftdi-ish)
# is a 'device' attribute on the object this is attached
# to, which has a 'port' property which is readable and
# writable.
[docs]class Bus(object):
"""
This class is a descriptor for a bus of a given width starting
at a given offset (0 = LSB). The device which does the actual
reading and writing is assumed to be a BitBangDevice instance
in the 'device' attribute of the object to which this is attached.
"""
[docs] def __init__(self, offset, width=1):
self.offset = offset
self.width = width
self._mask = ((1 << width) - 1)
def __get__(self, obj, type):
val = obj.device.port
return (val >> self.offset) & self._mask
def __set__(self, obj, value):
value = value & self._mask
# in a multi-threaded environment, would
# want to ensure following was locked, eg
# by acquiring a device lock
val = obj.device.port
val &= ~(self._mask << self.offset)
val |= value << self.offset
obj.device.port = val