Register.__getitem__ does not work for 64-bit wide registers

[soramichi]

PYNQ version: v2.5
Board name: PYNQ-Z1

When an overlay has 64-bit wide registers, the register_map member of the overlay cannot be elaborated due to the following error:

Traceback (most recent call last):
  File "./test.py", line 8, in <module>
    print(ip.register_map)
  File "/home/xilinx/pynq/registers.py", line 438, in __repr__
    "  {} = {}".format(k, repr(v)))
  File "/home/xilinx/pynq/registers.py", line 277, in __repr__
    return "Register(value={})".format(self[:])
  File "/home/xilinx/pynq/registers.py", line 166, in __getitem__
    return int((curr_val & mask) >> stop)
TypeError: ufunc 'right_shift' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

The mechanism behind is that type(curr_val & mask) becomes numpy.uint64 when mask does not fit within 32-bit, and numpy.uint64 somehow cannot be right-shifted as shown in this code:

>>> import numpy as np
>>> curr_val = np.uint32(1)
>>> mask = 18446744073709551615
>>> type(curr_val & mask)
<class 'numpy.uint64'>
>>> (curr_val & mask) >> 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: ufunc 'right_shift' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''
>>> 

On the other hand, when mask is smaller (e.g., 4294967294), typeof(curr_val & mask) is numpy.int64 (not uint), which can be right-sifted without an error.

[soramichi]

Update: it seems that stop should also be np.uint64 to conduct this shift operation.
https://stackoverflow.com/questions/30513741/python-bit-shifting-with-numpy

Adding the code below between L165 and L166 looks working. Should I submit a PR?

if isinstance(curr_val & mask, np.uint64):
    stop = np.uint64(stop)