Type:           Overlay
String form:    <pynq.pl.Overlay object at 0x31dcad30>
File:           /usr/local/lib/python3.4/dist-packages/pynq/pl.py
Docstring:
This class keeps track of a single bitstream's state and contents.

The overlay class holds the state of the bitstream and enables run-time
protection of bindlings.
Our definition of overlay is: "post-bitstream configurable design".
Hence, this class must expose configurability through content discovery
and runtime protection.

The IP dictionary stores the following information:
1. name (str), the key of an entry.
2. address (str), the base address of the IP.
3. range (str), the address range of the IP.
4. state (str), the state information about the IP.

The PS GPIO dictionary stores the following information:
1. name (str), the key of an entry.
2. pin (int), the user index of the GPIO, starting from 0.
3. state (str), the state information about the GPIO.

Attributes
----------
bitfile_name : str
    The absolute path of the bitstream.
bitstream : Bitstream
    The corresponding bitstream object.
ip_dict : dict
    The addressable IP instances on the overlay.
gpio_dict : dict
    The dictionary storing the PS GPIO pins.

Init docstring:
Return a new Overlay object.

An overlay instantiates a bitstream object as a member initially.

Note
----
This class requires a Vivado '.tcl' file to be next to bitstream file
with same base name (e.g. base.bit and base.tcl).

Parameters
----------
bitfile_name : str
    The bitstream name or absolute path as a string.