added start of 6510's IO port

src/main/kotlin/razorvine/c64emu/CpuIoPort.kt

@@ -0,0 +1,45 @@
+package razorvine.c64emu
+
+import razorvine.ksim65.Cpu6502
+import razorvine.ksim65.components.Address
+import razorvine.ksim65.components.MemMappedComponent
+import razorvine.ksim65.components.UByte
+
+/**
+ * The 6510's IO port located at $00/$01
+ * Controlling the memory layout, and cassette port (not processed at all).
+ * TODO: actually mapping the roms in and out of the address space. This requires some MMU type logic in the Bus class.
+ */
+class CpuIoPort(val cpu: Cpu6502) : MemMappedComponent(0x0000, 0x0001) {
+
+    private var dataDirections: Int = 0
+    private var ioPort: Int = 0
+    private var loram: Boolean = false  // Bit 0: LORAM signal.  Selects ROM or RAM at 40960 ($A000).  1=BASIC, 0=RAM
+    private var hiram: Boolean = false  // Bit 1: HIRAM signal.  Selects ROM or RAM at 57344 ($E000).  1=Kernal, 0=RAM
+    private var charen: Boolean = false // Bit 2: CHAREN signal.  Selects character ROM or I/O devices.  1=I/O, 0=ROM
+
+    override fun clock() { }
+    override fun reset() { }
+
+    override fun get(address: Address): UByte {
+        return if(address==0) dataDirections.toShort() else {
+            (ioPort or dataDirections.inv() and 0b00111111).toShort()
+        }
+    }
+
+    override fun set(address: Address, data: UByte) {
+        if(address==0) {
+            dataDirections = data.toInt()
+            determineRoms()
+        } else {
+            ioPort = data.toInt()
+            determineRoms()
+        }
+    }
+
+    private fun determineRoms() {
+        if (dataDirections and 0b00000001 != 0) loram = ioPort and 0b00000001 != 0
+        if (dataDirections and 0b00000010 != 0) hiram = ioPort and 0b00000010 != 0
+        if (dataDirections and 0b00000100 != 0) charen = ioPort and 0b00000100 != 0
+    }
+}

src/main/kotlin/razorvine/c64emu/Screen.kt

@@ -236,7 +236,7 @@ internal class Screen(private val chargenData: ByteArray, val ram: MemoryCompone
         // The vic 'sees' the charset rom at these addresses: $1000 + $1800, $9000 + $9800
         // so we can use pre-loaded images to efficiently draw the characters.
         // If the address is different, the vic takes charset data from RAM instead.
-        // TODO: currently custom charsets taken from RAM are not yet supported
+        // TODO: currently custom charsets taken from RAM aren't supported
         val shifted = charsetAddr and 0x0800 != 0
         var cached = coloredCharacterImageCache[Triple(char, color, shifted)]
         if (cached == null) {

src/main/kotlin/razorvine/c64emu/c64Main.kt

@@ -37,6 +37,7 @@ class C64Machine(title: String) : IVirtualMachine {
     val cia2 = Cia(2, 0xdd00, 0xddff, cpu)
     val basicRom = Rom(0xa000, 0xbfff).also { it.load(basicData) }
     val kernalRom = Rom(0xe000, 0xffff).also { it.load(kernalData) }
+    val cpuIoPort = CpuIoPort(cpu)
 
     private val debugWindow = DebugWindow(this)
     private val hostDisplay = MainC64Window(title, chargenData, ram, cpu, cia1)
@@ -53,6 +54,7 @@ class C64Machine(title: String) : IVirtualMachine {
         bus += vic
         bus += cia1
         bus += cia2
+        bus += cpuIoPort
         bus += ram
         bus += cpu
         bus.reset()