Compared to tests in the repository root, tests in the package have
many downsides:
* Unless explicitly excluded in find_packages(), tests and their
support code effectively become a part of public API.
This, unfortunately, happened with FHDLTestCase, which was never
intended for downstream use.
* Even if explicitly excluded from the setuptools package, using
an editable install, or setting PYTHONPATH still allows accessing
the tests.
* Having a sub-package that is present in the source tree but not
exported (or, worse, exported only sometimes) is confusing.
* The name `nmigen.test` cannot be used for anything else, such as
testing utilities that *are* intended for downstream use.
When a port component is skipped, it should appear neither in the RTL
nor in the constraint file. However, passing around components of
differential ports explicitly makes that harder.
Fixes#456.
Supersedes #457.
Co-authored-by: Jean THOMAS <git0@pub.jeanthomas.me>
Before this commit, it was possible to set and get clock constraints
placed on Pin objects. This was not a very good implementation, since
it relied on matching the identity of the provided Pin object to
a previously requested one. The only reason it worked like that is
deficiencies in nextpnr.
Since then, nextpnr has been fixed to allow setting constraints on
arbitrary nets. Correspondingly, backends that are using Synplify
were changed to use [get_nets] instead of [get_ports] in SDC files.
However, in some situations, Synplify does not allow specifying
ports in [get_nets]. (In fact, nextpnr had a similar problem, but
it has also been fixed.)
The simplest way to address this is to refer to the interior net
(after the input buffer), which always works. The only downside
of this is that requesting a clock as a raw pin using
platform.request("clk", dir="-")
and directly applying a constraint to it could fail in some cases.
This is not a significant issue.
Also, replace `bits, sign = x.shape()` with more idiomatic
`width, signed = x.shape()`.
This unifies all properties corresponding to `len(x)` to `x.width`.
(Not all values have a `width` property.)
Fixes#210.
This is useful for two reasons:
1. nMigen can provide better error messages than the platform and
do it earlier in the build pipeline.
2. Many platforms handle diffpairs by only constraining the P pin;
the N pin is completely ignored. If this is undetected,
downstream users (human or software) can rely on this
information assuming it is correct and introduce more errors.
(Of course, this will not catch every mistake, but the most
common is a copy-paste issue, and that will handle it.)
Fixes#124.
This adds the Clock() build DSL element, and adds a resource manager
function add_clock_constraint() that takes a Pin or a Signal.
Note that not all platforms, in particular not any nextpnr platforms
at the moment, can add constraints on arbitrary signals.
Fixes#86.
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.
This provides an escape hatch for the case where the nMigen platform
code is not flexible enough, and a IO buffer primitive needs to be
instantiated directly.
This is necessary because on some platforms, like iCE40, extras
become parameters on an IO primitive, since the constraint file
format is not expressive enough for all of them.
In the simple cases, a Pin record consisting of exactly one field
is equivalent in every way to this single field. In the more complex
case however, it can be used as a record, making the code more robust
such that it works with both bidirectional and unidirectional pins.
