This reverts commit 1634320c.

Bump emission to use FIRRTL 4.0.0.  Since Chisel is now emitting layer-colored
probes and the work-in-progress "enablelayer" keyword, Chisel needs to emit a
version of FIRRTL that compilers will accept.

The only change to the output (other than the stated version) is "groups" are
now changed to "layers".

Note: FIRRTL 4.0.0 is not finalized yet.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

This is an automated commit generated by the `circt/update-circt` GitHub
Action.

Co-authored-by: chiselbot <chiselbot@users.noreply.github.com>

Add a function that allows the layer to be "enabled" within the current
module scope.  This has the effect of emitting the module with the
"enablelayer <layer>" FIRRTL format.  This is not currently in the FIRRTL
spec---it is being prototyped inside CIRCT and is expected to land in the
spec soon.

This is done to allow for the use case of a Test Harness needing to enable
one or more layers (more than one layer is the union of several layers)
inside a DUT in order to drive it properly.  The specific use case is to
get access to an expensive core trace inside a microprocessor that is
hidden behind a layer.

This was originally written using an API where the layer provided a trait
that enabled the layer.  This runs afoul of Scala's restriction on
inheriting the same trait multiple times.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

This is in addition to the existing support in
Definition.apply. Sometimes it is not possible to use
Definition.apply, for example, if you plan to bore ports through the
Class being constructed. The new DynamicObject.apply method supports
this, and creates a DynamicObject from the newly elaborated Class.

Co-authored-by: Richard Xia <rxia@sifive.com>

This adds support for BoringUtils.bore to bore and connect Property
ports.

This adds an API to DataMirror to query if a Data is a Property.

Since we override litOption to always be None, we need to override
isLit to check the Binding.

Previously, it was not calling .ref. It was thus not properly:
1. Checking that the clock is bound hardware
2. Checking that the clock is visible in the current scope
3. Reifying the clock if its a view

Note that RegInit() was already correctly calling .ref.

Co-authored-by: Megan Wachs <megan@sifive.com>

curl seems to be more common and is included by default in MacOS whereas
wget is not.

Module's logic that creates the implicit clock and implicit reset within
the Module's body is now implemented in new traits that users are free
to mix in to RawModule. There are also now virtual methods implicitClock
and implicitReset that the user can override to change what clock or
reset is used.

Add OM test, support iterating fields of a OM object

Add a utility to reflect on the optional color of a layer.  This will be
used by libraries that need to know if they need to put generated logic in
a layerblock or not.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

Also fix some links in the README to point to local files or at least
the main branch rather than the old master branch.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

Extend the probe modifier case class, `ProbeInfo`, to include information
about the optional layer color of this layer.  Extend emission to properly
write this out to FIRRTL text.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

Add a memoized (via a `lazy val`) member to Layer that returns the FIRRTL
"full name" of that layer.  This includes all the parent layers prefixed
with interleaves periods.

This is memoized to avoid unnecessarily recomputing the partial prefixes
of parents.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

This ensures that the specific build tools show up in the Table of
Contents.

* Remove binary compatibility checking on 6.0.0
* Update .mergify.yml with 6.x (drop 3.5.x)
* Update PR Template (add 6.x, drop 3.5.x)