ctypes-bitfield 0.1

ctypes-bitfield provides a mechanism for creating ctypes compatible implementations of registers made up of bitfields. The base ctypes library already provides much of this functionality, but the ctypes-bitfield builder implementation wraps it up for simpler usage.

Normally the underlying register type would be a fixed size integer, a c_uint16 or c_uint64 or the like. However, a somewhat strange example usage would look something like this:

>>> from bitfield import *
>>> IEEE754 = make_bf('IEEE754', [
...             ('mantissa', c_uint, 23),
...             ('exponent', c_uint, 8),
...             ('sign', c_uint, 1)
... ], basetype=c_float, doc='Bitfields of an IEEE754 single precision float.')
>>> x = IEEE754()
>>> x.keys()
['mantissa', 'exponent', 'sign']
>>> x.base = 5.0
>>> list(x.items())     #doctest: +ELLIPSIS
[('mantissa', 2097152...), ('exponent', 129...), ('sign', 0...)]
>>> x.sign = 1
>>> x.base
-5.0
>>> x.exponent -= 2
>>> x.base
-1.25
>>> x.update(sign = 0, mantissa = 0)
>>> x.base
1.0

Bitfield objects are derived from ctypes.Union. Because of this derivation, these classes can be stacked into ctypes.Structures, which means they can work directly on memory mapped data. If the memory-mapped data is volatile, such as hardware registers, then the fact that the update() method operates on the entire register in one write, rather than one write per field, may be of use.

Works under Python 2.6+ and 3.0+

author:

Rob Gaddi, Highland Technology, Inc.

date:

08-May-2014

version:

0.1