RegField: separate UInt=>bytes and bytes=>regs

src/main/scala/uncore/tilelink2/RegField.scala

@@ -108,7 +108,7 @@ object RegField
 
   // Split a large register into a sequence of byte fields
   // The bytes can be individually written, as they are one byte per field
-  def bytes(x: UInt, base: Int = 0, beatBytes: Int = 4): Seq[RegField.Map] = {
+  def bytes(x: UInt): Seq[RegField] = {
     require (x.getWidth % 8 == 0)
     val bytes = Seq.tabulate(x.getWidth/8) { i => x(8*(i+1)-1, 8*i) }
     val wires = bytes.map { b => Wire(init = b) }
@@ -118,10 +118,15 @@ object RegField
         when (valid) { wires(i) := data }
         Bool(true)
       })
-    }.grouped(beatBytes).toSeq.zipWithIndex.map { case (reg, i) =>
-      (i+base, reg)
     }
   }
+
+  // Divide a long sequence of RegFields into a maximum sized registers
+  // Your input RegFields may not cross a beatBytes boundary!
+  def split(fields: Seq[RegField], base: Int, beatBytes: Int = 4): Seq[RegField.Map] = {
+    val offsets = fields.map(_.width).scanLeft(0)(_ + _).init
+    (offsets zip fields).groupBy(_._1 / (beatBytes*8)).toList.map(r => (r._1 + base, r._2.map(_._2)))
+  }
 }
 
 trait HasRegMap