ctypes-bitfield 0.2.6

bitfield

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 bitfield builder implementation wraps it up for simpler usage and avoids some of the quirky behaviors.

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.

remotestruct

remotstruct allows for ctypes derived classes, such as Structure and Bitfield, to be accessed over a remote interface, such as TCP/IP or a VME indirection scheme. Effectively, this means turning requests for elements of the structure into requests for arbitrary byte sequences, fetching them, and managing the translation.

If, for instance, you had a mechanism whereby, over an Ethernet socket, you could write 8 bytes to address 0x100 as W 0x100 55 45 10 18 26 28 33 47, then read back four of those bytes by sending R 0x100 4 and getting back 55 45 10 18 (all of that newline delimited), then you would write a protocol handler:

>>> class SerialHandler(object):
...    def __init__(self, sock):
...        self.sock = sock
...
...    def writeBytes(self, addr, data):
...        msg = "W " + hex(addr) + ' '.join(str(d) for d in data)
...        self.sock.sendall(msg.encode('ascii'))
...
...    def readBytes(self, addr, size):
...        msg = "R 0x{0:X} {1}".format(addr, size)
...        self.sock.sendall(msg.encode('ascii'))
...
...        received = []
...        while True:
...            x = self.sock.recv(4096)
...            received.append(x)
...            if b'\n' in x:
...                break
...
...        msg = b''.join(received)
...        data = bytes(int(b) for b in msg.split(b' '))
...        return data

>>> class DataStructure(Structure):
...     _fields_ = [
...         ('flags', c_uint32),
...         ('_dummy1', c_uint32),
...         ('offset', c_int32),
...         ('slope', c_float)
...     ]

>>> sock = socket.create_connection(('1.2.3.4', 80))
>>> handler = SerialHandler(sock)
>>> rs = remotestruct.Remote(DataStructure, handler)
>>> rs.flags
5
>>> rs.flags = 183
>>> rs.flags
183

Works under Python 2.6+ and 3.0+

author:

Rob Gaddi, Highland Technology, Inc.

date:

02-Sep-2014

version:

0.2.6