Source code for pynq.lib.pmod.pmod_cable

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from . import Pmod_IO
from . import PMOD_DIO_DATA_OFFSET

__author__ = "Yun Rock Qu"
__email__ = "pynq_support@xilinx.com"

[docs]class Pmod_Cable(Pmod_IO):
"""This class can be used for a cable connecting Pmod interfaces.

This class inherits from the Pmod IO class.

Note
----
When 2 Pmods are connected using a cable, the parameter 'cable' decides
whether the cable is a 'loopback' or 'straight' cable.
The default is a straight cable (no internal wire twisting).
For pin mapping, please check the Pmod IO class.

Attributes
----------
microblaze : Pmod
Microblaze processor instance used by this module.
index : int
The index of the Pmod pin, from 0 to 7.
direction : str
Input 'in' or output 'out'.
cable : str
Either 'straight' or 'loopback'.

"""
def __init__(self, mb_info, index, direction, cable):
"""Return a new instance of a Cable object.

Only the cable type is checked during initialization, since all the
other parameters are checked by Pmod IO class.

Parameters
----------
mb_info : dict
A dictionary storing Microblaze information, such as the
IP name and the reset name.
index: int
The index of the pin in a Pmod, from 0 to 7.
direction : str
Input 'in' or output 'out'.
cable : str
Either 'straight' or 'loopback'.

"""
if cable not in ['straight', 'loopback']:
raise ValueError("Cable can only be 'straight', or 'loopback'.")

super().__init__(mb_info, index, direction)
self.cable = cable

[docs]    def set_cable(self, cable):
"""Set the type for the cable.

Note
----------
The default cable type is 'straight'. Only straight cable or loop-back
cable can be recognized.

Parameters
----------
cable : str
Either 'straight' or 'loopback'.

Returns
-------
None

"""
if cable not in ['straight', 'loopback']:
raise ValueError("Cable can only be 'straight', or 'loopback'.")
self.cable = cable

"""Receive the value from the Pmod cable.

This method overrides the read() method in the Pmod IO class.
There are no new write() method defined in this class, so
the read() will be inherited from Pmod IO class.

Note
----
Only use this function when direction = 'in'.

When two Pmods are connected on the same board, for any received raw
value, a "straignt" cable flips the upper 4 pins and the lower 4 pins:
A Pmod interface       <=>      Another Pmod interface
{vdd,gnd,3,2,1,0}      <=>      {vdd,gnd,7,6,5,4}
{vdd,gnd,7,6,5,4}      <=>      {vdd,gnd,3,2,1,0}

A "loop-back" cable satisfies the following mapping
between two Pmods:
A Pmod interface       <=>      Another Pmod interface
{vdd,gnd,3,2,1,0}      <=>      {vdd,gnd,3,2,1,0}
{vdd,gnd,7,6,5,4}      <=>      {vdd,gnd,7,6,5,4}

Returns
-------
int
The data (0 or 1) on the specified Pmod IO pin.

"""