bricoleur commit

src/test/scala/RISCV/testRunner.scala

@@ -164,54 +164,7 @@ object TestRunner {
 
         helper(events, initState)
       }
-
-
-      def nBitPredictor(events: List[BranchEvent]): Int = {
-
-        case class nBitPredictor(
-          values          : List[Int],
-          predictionRules : List[Boolean],
-          transitionRules : Int => Boolean => Int,
-        ){
-          val slots = values.size
-
-          def predict(pc: Int): Boolean = predictionRules(values(pc.getTag(slots)))
-
-          def update(pc: Int, taken: Boolean): nBitPredictor = {
-            val current = values(pc.getTag(slots))
-            copy(values = values.updated(pc.getTag(slots), transitionRules(current)(taken)))
-          }
-        }
-
-        val initPredictor = nBitPredictor(
-          List.fill(4)(0),
-          List(
-            false,
-            false,
-            true,
-            true,
-          ),
-          r => r match {
-            case 0 => taken => if(taken) 1 else 0
-            case 1 => taken => if(taken) 3 else 0
-            case 2 => taken => if(taken) 3 else 0
-            case 3 => taken => if(taken) 3 else 2
-          }
-        )
-
-        events.foldLeft((0, initPredictor)){ case(((acc, bp), event)) => event match {
-          case Taken(pc, _) if bp.predict(pc)  => (acc,     bp.update(pc, true))
-          case Taken(pc, _)                    => (acc + 1, bp.update(pc, false))
-          case NotTaken(pc) if !bp.predict(pc) => (acc,     bp.update(pc, false))
-          case NotTaken(pc)                    => (acc + 1, bp.update(pc, true))
-        }}._1
-      }
-
-
-
       say(OneBitInfiniteSlots(events))
-      say(nBitPredictor(events))
-
     }
 
     true

theory2.org

@@ -95,7 +95,7 @@
    #+end_src
 
 * Question 3 - Branch prediction
-  Consider a 2 bit branch predictor with only 4 slots for a 32 bit architecture, where the decision to 
+  Consider a 2 bit branch predictor with only 4 slots for a 32 bit architecture (without BTB), where the decision to 
   take a branch or not is decided in accordance to the following table:
   #+begin_src text
   state  ||  predict taken  ||  next state if taken  ||  next state if not taken ||
@@ -137,8 +137,8 @@
 
   #+BEGIN_SRC scala
   sealed trait BranchEvent
-  case class Taken(addr: Int) extends BranchEvent
-  case class NotTaken(addr: Int) extends BranchEvent
+  case class Taken(from: Int, to: Int) extends BranchEvent
+  case class NotTaken(at: Int) extends BranchEvent
 
 
   def profile(events: List[BranchEvent]): Int = ???
@@ -170,11 +170,11 @@
 	// `case Constructor(arg1, arg2) :: t => if(p(arg1, arg2))`
 	// means we want to match a list whose first element is of type Constructor while satisfying some predicate p,
 	// called an if guard.
-	case Taken(addr)    :: t if( predictionTable(addr)) => helper(t, predictionTable)
-	case Taken(addr)    :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, true))
-	case NotTaken(addr) :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, false))
-	case NotTaken(addr) :: t if( predictionTable(addr)) => helper(t, predictionTable)
-	case _ => 0
+        case Taken(from, to) :: t if( predictionTable(from)) => helper(t, predictionTable)
+        case Taken(from, to) :: t if(!predictionTable(from)) => 1 + helper(t, predictionTable.updated(from, true))
+        case NotTaken(addr)  :: t if(!predictionTable(addr)) => 1 + helper(t, predictionTable.updated(addr, false))
+        case NotTaken(addr)  :: t if( predictionTable(addr)) => helper(t, predictionTable)
+        case _ => 0
       }
     }
 
@@ -191,14 +191,19 @@
 ** Your task
    Your job is to implement a test that checks how many misses occur for a 2 bit branch predictor with 8 slots.
    The rule table is the same as in question 3.
-   For simplicitys sake, assume that every value in the table is initialized to 00.
+   The predictor does not use a branch target buffer (BTB), which means that the address will always be decoded in
+   the ID stage.
+   For you this means you do not need to keep track of branch targets, simplifying your simulation quite a bit.
+   (If not you would need to add logic for when BTB value does not match actual value)
+
+   For simplicity's sake, assume that every value in the table is initialized to 00.
 
    For this task it is necessary to use something more sophisticated than ~Map[(Int, Boolean)]~ to represent
    your branch predictor model.
 
    The skeleton code is located in ~testRunner.scala~ and can be run using testOnly FiveStage.ProfileTest.
 
-   With a 2 bit 4 slot scheme, how many misses will you incur?
+   With a 2 bit 8 slot scheme, how many mispredicts will happen?
    Answer with a number.
 
 * Question 5 - Cache profiling