Printf: Add support for tabs, and give helpful error messages (#1323) (…

…#1326)

Co-authored-by: Megan Wachs <megan@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

chiselFrontend/src/main/scala/chisel3/Printf.scala

@@ -19,13 +19,15 @@ object printf { // scalastyle:ignore object.name
     require(formatIn forall (c => c.toInt > 0 && c.toInt < 128),
       "format strings must comprise non-null ASCII values")
     def escaped(x: Char) = {
-      require(x.toInt >= 0)
+      require(x.toInt >= 0, s"char ${x} to Int ${x.toInt} must be >= 0")
       if (x == '"' || x == '\\') {
         s"\\${x}"
       } else if (x == '\n') {
         "\\n"
+      } else if (x == '\t') {
+        "\\t"
       } else {
-        require(x.toInt >= 32) // TODO \xNN once FIRRTL issue #59 is resolved
+        require(x.toInt >= 32, s"char ${x} to Int ${x.toInt} must be >= 32") // TODO \xNN once FIRRTL issue #59 is resolved
         x
       }
     }

src/test/scala/chiselTests/PrintableSpec.scala

@@ -95,6 +95,16 @@ class PrintableSpec extends FlatSpec with Matchers {
       case e => fail()
     }
   }
+  it should "correctly emit tab" in {
+    class MyModule extends BasicTester {
+      printf(p"\t")
+    }
+    val firrtl = Driver.emit(() => new MyModule)
+    getPrintfs(firrtl) match {
+      case Seq(Printf("\\t", Seq())) =>
+      case e => fail()
+    }
+  }
   it should "support names of circuit elements including submodule IO" in {
     // Submodule IO is a subtle issue because the Chisel element has a different
     // parent module