TLRegMapper: emit a JSON file describing the register fields

build.sbt

@@ -15,6 +15,7 @@ lazy val commonSettings = Seq(
   traceLevel   := 15,
   scalacOptions ++= Seq("-deprecation","-unchecked"),
   libraryDependencies ++= Seq("org.scala-lang" % "scala-reflect" % scalaVersion.value),
+  libraryDependencies ++= Seq("org.json4s" %% "json4s-jackson" % "3.5.0"),
   addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)
 )
 
@@ -44,3 +45,4 @@ val chipSettings = Seq(
     s"make -C $makeDir  -j $jobs $target".!
   }
 )
+

src/main/scala/tilelink/RegisterRouter.scala

@@ -7,9 +7,12 @@ import freechips.rocketchip.config.Parameters
 import freechips.rocketchip.diplomacy._
 import freechips.rocketchip.regmapper._
 import freechips.rocketchip.interrupts._
-import freechips.rocketchip.util.HeterogeneousBag
+import freechips.rocketchip.util.{HeterogeneousBag, ElaborationArtefacts}
 import scala.math.{min,max}
 
+import org.json4s.JsonDSL._
+import org.json4s.jackson.JsonMethods.{pretty, render}
+
 case class TLRegisterNode(
     address:     Seq[AddressSet],
     device:      Device,
@@ -80,6 +83,36 @@ case class TLRegisterNode(
     bundleIn.b.valid := Bool(false)
     bundleIn.c.ready := Bool(true)
     bundleIn.e.ready := Bool(true)
+
+    // Dump out the register map for documentation purposes.
+    val registerDescriptions = mapping.map { case (offset, seq) =>
+      var currentBitOffset = 0
+      s"regAt0x${offset.toHexString}" -> (
+        ("description"    ->  "None Provided") ~
+        ("addressOffset"  -> s"0x${offset.toHexString}") ~
+          ("fields" -> seq.zipWithIndex.map { case (f, i) => {
+            val tmp = (f.description.map{ _.displayName }.getOrElse(s"unnamedRegField${i}") -> (
+              ("description" -> f.description.map{_.description}.getOrElse("No Description Provided")) ~
+                ("bitOffset"   -> currentBitOffset) ~
+                ("bitWidth"    -> f.width) ~
+                ("resetMask"   -> f.description.map { d => if (d.resetType != RegFieldResetType.N) "all" else "none"}.getOrElse("none")) ~
+                ("resetValue"  -> f.description.map { _.resetValue}.getOrElse(0)) ~
+                ("headerName"  -> f.description.map { _.headerName}.getOrElse(""))))
+            currentBitOffset = currentBitOffset + f.width
+            tmp
+          }}))}
+
+    val simpleDev = device.asInstanceOf[SimpleDevice]
+    val base = s"0x${address.head.base.toInt.toHexString}"
+    val json = ("peripheral" -> (
+      ("displayName" -> s"deviceAt${base}") ~
+      ("description" -> s"None Provided") ~
+      ("baseAddress" -> base) ~
+      ("regWidth" -> beatBytes) ~
+      ("access" -> "rw") ~ // specified at field level
+      ("registers" -> registerDescriptions)
+    ))
+    ElaborationArtefacts.add(s"${base}.regmap.json", pretty(render(json)))
   }
 }