Add Support for FPGA Bitstream Preset-registers (#1050)

Introduce Preset Register Specialized Emission
- Introduce EmissionOption trait
- Introduce PresetAnnotation & PresetRegAnnotation
- Enable the collection of Annotations in the Emitter
- Introduce collection mechanism for EmissionOptions in the Emitter
- Add PropagatePresetAnnotation transform to annotate register for emission and clean-up the useless reset tree (no DCE involved)
- Add corresponding tests spec and tester

Co-authored-by: Jack Koenig <koenig@sifive.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/src/main/scala/firrtl/annotations/PresetAnnotations.scala b/src/main/scala/firrtl/annotations/PresetAnnotations.scala
new file mode 100644
index 00000000..727417c1
--- /dev/null
+++ b/src/main/scala/firrtl/annotations/PresetAnnotations.scala
@@ -0,0 +1,33 @@
+// See LICENSE for license details.
+
+package firrtl
+package annotations
+
+/**
+  * Transform all registers connected to the targeted AsyncReset tree into bitstream preset registers
+  * Impacts all registers connected to any child (cross module) of the target AsyncReset
+  *
+  * @param target ReferenceTarget to an AsyncReset
+  */
+case class PresetAnnotation(target: ReferenceTarget)
+    extends SingleTargetAnnotation[ReferenceTarget] with firrtl.transforms.DontTouchAllTargets {
+  override def duplicate(n: ReferenceTarget) = this.copy(target = n)
+}
+
+
+/**
+  * Transform the targeted asynchronously-reset Reg into a bitstream preset Reg
+  * Used internally to annotate all registers associated to an AsyncReset tree
+  *
+  * @param target ReferenceTarget to a Reg
+  */
+private[firrtl] case class PresetRegAnnotation(
+  target: ReferenceTarget
+) extends SingleTargetAnnotation[ReferenceTarget] with RegisterEmissionOption {
+  def duplicate(n: ReferenceTarget) = this.copy(target = n)
+  override def useInitAsPreset = true
+  override def disableRandomization = true
+}
+
+
+