1eee7cd76f
Although a dir="oe" pin is generally equivalent to dir="io" pin with the i* signal(s) disconnected, they are not equivalent, because some pins may not be able to support input buffers at all, either because there are no input buffers, or because the input buffers are consumed by some other resource. E.g. this can happen on iCE40 when the input buffer is consumed by a PLL.
98 lines
4 KiB
Python
98 lines
4 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", "oe", "io"):
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raise TypeError("Direction must be one of \"i\", \"o\", \"io\", or \"oe\", not '{!r}'"""
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.format(dir))
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if not isinstance(xdr, int) or xdr < 0:
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raise TypeError("Gearing ratio must be a non-negative 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 in (0, 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", "oe", "io"):
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if xdr in (0, 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 in ("oe", "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"``, ``"oe"``
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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 ``"oe"`` is
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specified, the ``o``/``oN`` signals are present, and an ``oe`` signal is present.
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If ``"io"`` is specified, both the ``i``/``iN`` and ``o``/``oN`` signals are present, and
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an ``oe`` signal is present.
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xdr : int
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Gearbox ratio. If equal to 0, the I/O buffer is combinatorial, and only ``i``/``o``
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signals are present. 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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name : str
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Name of the underlying record.
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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 0 or 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 0 or 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"`` or ``dir="oe"``. Buffers generally
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cannot change direction more than once per cycle, so at most one output enable signal
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is present.
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"""
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def __init__(self, width, dir, xdr=0, name=None):
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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), name=name)
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