18% speedup from interrupt optimization

src/main/kotlin/Main.kt

@@ -18,15 +18,16 @@ fun main(args: Array<String>) {
         cpu.loadAbs(File(args[0]))
         cpu.runState = CPU.RunState.RUNNING
         cpu.pc = 0x80u
-	val start = System.nanoTime()
-        val ninsn = cpu.run()
-	val end = System.nanoTime()
+        val start = System.nanoTime()
+        val ninsn = cpu.run(50000000)
+        val end = System.nanoTime()
 
         System.err.println("Halted at 0${cpu.pc.toString(8)}")
-	val time = (end-start).toDouble() / 1_000_000_000.0
-	println("Executed ${ninsn} in ${time}s: ${ninsn/time} i/s")
+        val time = (end - start).toDouble() / 1_000_000_000.0
+        println("Executed ${ninsn} in ${time}s: ${ninsn / time} i/s")
     } finally {
         println("Exiting")
         console.stop()
     }
+    System.exit(0)
 }

src/main/kotlin/com/thequux/mcpdp/core/CPU.kt

@@ -111,11 +111,11 @@ class CPU(val mbus: MemBus) {
 	    val bitset = pirq shr 8
 	    var maxp: UShort = 0u
 	    for (i in 7 downTo 1) {
-		if (bitset bit i) {
-		    maxp = i.toUShort() shl 1
-		    break
-		}
-	    }
+            if (bitset bit i) {
+                maxp = i.toUShort() shl 1
+                break
+            }
+        }
 	    field = value and 0xFE00u or maxp or (maxp shl 4)
 	}
 
@@ -828,21 +828,28 @@ class CPU(val mbus: MemBus) {
         try {
             if (runState == RunState.HALTED) return
 
-            for (i in 7 downTo (psw_priority + 1)) {
-                if (pirq bit 8+i) {
-                    logger.debug("PIRQ{} trap to 0xA0", i)
-                    trap(0xA0u)
-                    break
+            if (mbus.unibus.interruptPending) {
+                for (i in 7 downTo (psw_priority + 1)) {
+                    if (pirq bit 8 + i) {
+                        logger.debug("PIRQ{} trap to 0xA0", i)
+                        trap(0xA0u)
+                        break
+                    }
+                    val source = mbus.unibus.checkInterrupt(i)
+                    if (source != null) {
+                        // we might have been waiting for an interrupt
+                        runState = RunState.RUNNING
+                        val vector = source.vector
+                        logger.debug("Unibus interrupt at pri {} to {}", i, vector)
+                        trap(vector)
+                        source.handled()
+                        break
+                    }
                 }
-                val source = mbus.unibus.checkInterrupt(i)
-                if (source != null) {
-                    // we might have been waiting for an interrupt
-                    runState = RunState.RUNNING
-                    val vector = source.vector
-                    logger.debug("Unibus interrupt at pri {} to {}", i, vector)
-                    trap(vector)
-                    source.handled()
-                    break
+            } else {
+                val pirqLvl = pirq.toInt() shr 1 and 7;
+                if (pirqLvl > psw_priority) {
+                    trap(0xA0u)
                 }
             }
             if (runState == RunState.WAIT_FOR_INTERRUPT) {
@@ -865,12 +872,21 @@ class CPU(val mbus: MemBus) {
     }
 
     fun run(): Long {
-    	var ninsn: Long = 0
+        var ninsn: Long = 0
         while (runState == RunState.RUNNING) {
-	    ninsn++
+            ninsn += run(Long.MAX_VALUE)
             step()
         }
-	return ninsn
+        return ninsn
+    }
+
+    fun run(nstep: Long): Long {
+        var ninsn: Long = 0
+        while (runState == RunState.RUNNING && ninsn < nstep) {
+            ninsn++
+            step()
+        }
+        return ninsn
     }
 
     fun trap(vector: UShort) {

src/main/kotlin/com/thequux/mcpdp/peripheral/Unibus.kt

@@ -77,6 +77,9 @@ class Unibus: PAddressSpace, Subregion(12, 6) {
     private val logger = LoggerFactory.getLogger(this.javaClass)
 
     private val queue: Array<MutableList<InterruptSource>> = Array(8) { Vector(4) }
+    private var interruptCount: Int = 0
+    val interruptPending: Boolean
+        get() = interruptCount > 0
 
     override fun map(address: UInt): PAddressSpace =
         super.map(address) ?: throw BusTimeoutError(address)
@@ -101,11 +104,17 @@ class Unibus: PAddressSpace, Subregion(12, 6) {
     /// to fetch the currently desired interrupt vector
     fun assertInterrupt(priority: Int, device: InterruptSource) {
         val list = queue[priority]
+        if (list.isEmpty()) {
+            interruptCount++
+        }
         if (!list.contains(device)) list.add(device)
     }
 
     fun deassertInterrupt(priority: Int, device: InterruptSource) {
-        queue[priority].remove(device)
+        val lvlQueue = queue[priority]
+        if (lvlQueue.remove(device) && lvlQueue.isEmpty()) {
+            interruptCount--
+        }
     }
 
     // Checks for an interrupt. The handler receives (priority, device)