regmapper: refactor how json is emitted

src/main/scala/regmapper/Annotation.scala

@@ -0,0 +1,23 @@
+// See LICENSE.SiFive for license details.
+
+package freechips.rocketchip.regmapper
+
+import org.json4s.JsonDSL._
+import org.json4s.jackson.JsonMethods.{pretty, render}
+
+object RegMappingAnnotation {
+  def serialize(base: BigInt, name: String, mapping: RegField.Map*): String = {
+    val regDescs = mapping.flatMap { case (byte, seq) =>
+      seq.map(_.width).scanLeft(0)(_ + _).zip(seq).map { case (bit, f) =>
+        val anonName = s"unnamedRegField${byte.toHexString}_${bit}"
+        (f.desc.map{ _.name}.getOrElse(anonName)) -> f.toJson(byte, bit)
+      }
+    }
+
+    pretty(render(
+      ("peripheral" -> (
+        ("displayName" -> name) ~
+        ("baseAddress" -> s"0x${base.toInt.toHexString}") ~
+        ("regfields" -> regDescs)))))
+  }
+}