93 lines
3.6 KiB
Python
93 lines
3.6 KiB
Python
from .. import *
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from ..hdl.rec import *
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__all__ = ["pin_layout", "Pin"]
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def pin_layout(width, dir, xdr=1):
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"""
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Layout of the platform interface of a pin or several pins, which may be used inside
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user-defined records.
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See :class:`Pin` for details.
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"""
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if not isinstance(width, int) or width < 1:
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raise TypeError("Width must be a positive integer, not '{!r}'"
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.format(width))
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if dir not in ("i", "o", "io"):
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raise TypeError("Direction must be one of \"i\", \"o\" or \"io\", not '{!r}'"""
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.format(dir))
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if not isinstance(xdr, int) or xdr < 1:
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raise TypeError("Gearing ratio must be a positive integer, not '{!r}'"
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.format(xdr))
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fields = []
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if dir in ("i", "io"):
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if xdr == 1:
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fields.append(("i", width))
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else:
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for n in range(xdr):
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fields.append(("i{}".format(n), width))
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if dir in ("o", "io"):
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if xdr == 1:
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fields.append(("o", width))
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else:
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for n in range(xdr):
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fields.append(("o{}".format(n), width))
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if dir == "io":
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fields.append(("oe", 1))
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return Layout(fields)
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class Pin(Record):
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"""
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An interface to an I/O buffer or a group of them that provides uniform access to input, output,
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or tristate buffers that may include a 1:n gearbox. (A 1:2 gearbox is typically called "DDR".)
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A :class:`Pin` is identical to a :class:`Record` that uses the corresponding :meth:`pin_layout`
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except that it allos accessing the parameters like ``width`` as attributes. It is legal to use
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a plain :class:`Record` anywhere a :class:`Pin` is used, provided that these attributes are
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not necessary.
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Parameters
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----------
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width : int
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Width of the ``i``/``iN`` and ``o``/``oN`` signals.
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dir : ``"i"``, ``"o"``, ``"io"``
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Direction of the buffers. If ``"i"`` is specified, only the ``i``/``iN`` signals are
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present. If ``"o"`` is specified, only the ``o``/``oN`` signals are present. If ``"io"``
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is specified, both the ``i``/``iN`` and ``o``/``oN`` signals are present, and an ``oe``
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signal is present.
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xdr : int
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Gearbox ratio. If equal to 1, the I/O buffer is SDR, and only ``i``/``o`` signals are
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present. If greater than 1, the I/O buffer includes a gearbox, and ``iN``/``oN`` signals
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are present instead, where ``N in range(0, N)``. For example, if ``xdr=2``, the I/O buffer
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is DDR; the signal ``i0`` reflects the value at the rising edge, and the signal ``i1``
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reflects the value at the falling edge.
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Attributes
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----------
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i : Signal, out
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I/O buffer input, without gearing. Present if ``dir="i"`` or ``dir="io"``, and ``xdr`` is
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equal to 1.
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i0, i1, ... : Signal, out
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I/O buffer inputs, with gearing. Present if ``dir="i"`` or ``dir="io"``, and ``xdr`` is
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greater than 1.
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o : Signal, in
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I/O buffer output, without gearing. Present if ``dir="o"`` or ``dir="io"``, and ``xdr`` is
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equal to 1.
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o0, o1, ... : Signal, in
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I/O buffer outputs, with gearing. Present if ``dir="o"`` or ``dir="io"``, and ``xdr`` is
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greater than 1.
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oe : Signal, in
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I/O buffer output enable. Present if ``dir="io"``. Buffers generally cannot change
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direction more than once per cycle, so at most one output enable signal is present.
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"""
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def __init__(self, width, dir, xdr=1):
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self.width = width
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self.dir = dir
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self.xdr = xdr
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super().__init__(pin_layout(self.width, self.dir, self.xdr))
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