Fix ldk instruction timing bug.

nyancient · Jan 1, 2022 · 2008c7d · 2008c7d
1 parent 27918a7
commit 2008c7d
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Showing 3 changed files with 19 additions and 6 deletions.
diff --git a/README.md b/README.md
@@ -5,4 +5,4 @@ a [Korone](https://twitter.com/KoroneNoises/)-based sound chip.
 ## Usage
 1. Download the JAR from the [latest release](https://github.com/foxolotl/koro8/releases/latest).
 2. Get some [roms](https://github.com/loktar00/chip8/tree/master/roms) to run.
-3. Run koro8 with the path to one of your downloaded roms as argument: `java -jar koro8-0.1-min.jar /path/to/some/rom.ch8`
+3. Run koro8 with the path to one of your downloaded roms as argument: `java -jar koro8-0.1.1-min.jar /path/to/some/rom.ch8`
diff --git a/build.gradle.kts b/build.gradle.kts
@@ -6,7 +6,7 @@ plugins {
 }
 
 group = "com.github.foxolotl"
-version = "0.1"
+version = "0.1.1"
 
 repositories {
     mavenCentral()

diff --git a/src/main/kotlin/com/github/foxolotl/koro8/CPU.kt b/src/main/kotlin/com/github/foxolotl/koro8/CPU.kt
@@ -24,6 +24,7 @@ class CPU(
     private val cycleTimeNanos: Long = 1000000000L / cyclesPerSecond
     private val cycleSleepMillis: Long = cycleTimeNanos / 1000000L
     private var cycles: Long = 0
+    private var nextCycleDeadline: Long = 0
 
     private val heap: Heap = Heap(HEAP_SIZE)
     private val stack: Stack = Stack(STACK_SIZE)
@@ -74,7 +75,12 @@ class CPU(
         display.clear()
     }
 
-    tailrec fun run(ticks: Long = Long.MAX_VALUE, nextCycleDeadline: Long = System.nanoTime()) {
+    fun run(ticks: Long = Long.MAX_VALUE) {
+        nextCycleDeadline = System.nanoTime()
+        execute(ticks)
+    }
+
+    private tailrec fun execute(ticks: Long) {
         if (ticks == 0L) {
             return
         }
@@ -84,10 +90,11 @@ class CPU(
         val now = System.nanoTime()
         if (now >= nextCycleDeadline) {
             step()
-            run(ticks - 1, nextCycleDeadline + cycleTimeNanos)
+            nextCycleDeadline += cycleTimeNanos
+            execute(ticks - 1)
         } else {
             Thread.sleep(cycleSleepMillis)
-            run(ticks, nextCycleDeadline)
+            execute(ticks)
         }
     }
 
@@ -152,7 +159,13 @@ class CPU(
         }
     }
 
-    private inline fun ldk(reg: Register) = ld(reg, keyboard.waitKey())
+    private inline fun ldk(reg: Register) {
+        val t0 = System.nanoTime()
+        val key = keyboard.waitKey()
+        val t1 = System.nanoTime()
+        nextCycleDeadline += (t1 - t0)
+        ld(reg, key)
+    }
     private inline fun stdt(reg: Register) = ld(reg, regs.DT)
     private inline fun ld(reg1: Register, reg2: Register) = ld(reg1, regs.V[reg2])
     private inline fun sne(reg1: Register, reg2: Register) = sne(reg1, regs.V[reg2])