1 files changed, 7 insertions, 8 deletions
diff --git a/src/main/scala/Chisel/internal/firrtl/IR.scala b/src/main/scala/Chisel/internal/firrtl/IR.scala
index beb32e6c..4c039e9a 100644
--- a/src/main/scala/Chisel/internal/firrtl/IR.scala
+++ b/src/main/scala/Chisel/internal/firrtl/IR.scala
@@ -167,16 +167,15 @@ case class Port(id: Data, dir: Direction)
 case class Printf(clk: Arg, formatIn: String, ids: Seq[Arg]) extends Command {
   require(formatIn.forall(c => c.toInt > 0 && c.toInt < 128), "format strings must comprise non-null ASCII values")
   def format: String = {
-    def escaped(x: Char) =
-      if (x == '"' || x == '\\' || x == '?') {
-        "\\" + x
-      } else if (x == '\n') {
-        "\\n"
-      } else if (x.toInt < 32) {
-        s"\\x${BigInt(x.toInt).toString(16)}"
-      } else {
+    def escaped(x: Char) = {
+      require(x.toInt >= 0)
+      if (x == '"' || x == '\\') s"\\${x}"
+      else if (x == '\n') "\\n"
+      else {
+        require(x.toInt >= 32) // TODO \xNN once FIRRTL issue #59 is resolved
         x
       }
+    }
     formatIn.map(escaped _).mkString
   }
 }