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docs: correct description of requirements in docstring of wiring.connect #1473

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docs: correct description of requirements in docstring of wiring.connect #1473

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26 changes: 14 additions & 12 deletions amaranth/lib/wiring.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1363,23 +1363,25 @@ def connect(m, *args, **kwargs):

The connections can be made only if all of the objects satisfy a number of requirements:

* Every interface object must have the same set of port members, and they must have the same
:meth:`dimensions <Member.dimensions>`.
* Every interface object must have the same set of port members.
* For a given path, if one of the interface objects has an output port member, then all
interface objects must have the same :meth:`dimensions <Member.dimensions>`.
* For each path, the port members of every interface object must have the same width and initial
value (for port members corresponding to signals) or constant value (for port members
corresponding to constants). Signedness may differ.
* For each path, at most one interface object must have the corresponding port member be
value. Signedness may differ.
* For each path, at most one interface object can have the corresponding port member be
an output.
* For a given path, if any of the interface objects has an input port member corresponding
to a constant value, then the rest of the interface objects must have output port members
corresponding to the same constant value.
* For a given path, if any of the interface objects have an input port member corresponding
to a constant value, and one of the interface objects has an output port member, then the
output port member must correspond to the same constant value.
* When connecting multiple interface objects, at least one connection must be made.

For example, if :py:`obj1` is being connected to :py:`obj2` and :py:`obj3`, and :py:`obj1.a.b`
is an output, then :py:`obj2.a.b` and :py:`obj2.a.b` must exist and be inputs. If :py:`obj2.c`
is an input and its value is :py:`Const(1)`, then :py:`obj1.c` and :py:`obj3.c` must be outputs
whose value is also :py:`Const(1)`. If no ports besides :py:`obj1.a.b` and :py:`obj1.c` exist,
then no ports except for those two must exist on :py:`obj2` and :py:`obj3` either.
is an output, then :py:`obj2.a.b` and :py:`obj3.a.b` must exist and be inputs. If :py:`obj2.c`
is an input and its value is :py:`Const(1)`, and :py:`obj1.c` in an output, then the value of
:py:`obj1.c` must also be :py:`Const(1)`. Also :py:`obj3.c` may be a non-constant input, or it
may be an input with a value of :py:`Const(1)`. If no ports besides :py:`obj1.a.b` and
:py:`obj1.c` exist, then no ports except for those two must exist on :py:`obj2` and :py:`obj3`
either.

Once it is determined that the interface objects can be connected, this function performs
an equivalent of:
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