'Performs a single load.'

def _single_load(self, addr, offset, size):

    try:
        d = self._contents[addr]
    except KeyError:
        d = self._handle_uninitialized_read(addr)
        self._contents[addr] = d
    if ((offset == 0) and (size == self.width)):
        return d
    else:
        return d.get_bytes(offset, size)
