diff --git a/src/d6502/base.d b/src/d6502/base.d
index e33dce2..1085e19 100644
--- a/src/d6502/base.d
+++ b/src/d6502/base.d
@@ -135,14 +135,26 @@ class CpuBase(bool strict, bool cumulative)
         restore([0, 0, 0, 0, 0, 0xFF, 0, 0, 0, 0, 0, 1]);
     }
 
-    ubyte delegate(ushort addr) memoryRead;
-    void delegate(ushort addr, ubyte val) memoryWrite;
+    struct _Mem
+    {
+        ubyte delegate(ushort addr) read;
+        void delegate(ushort addr, ubyte val) write;
+    }
+    _Mem memory;
+
+    struct _Clock
+    {
+        static if (cumulative)
+            void delegate(int cycles) tick;
+        else
+            void delegate() tick;
+    }
+    _Clock clock;
+
     debug(disassemble)
     {
         string delegate(ushort addr) memoryName;
     }
-    static if (cumulative) void delegate(int cycles) tick;
-    else  void delegate() tick;
 
     abstract void run(bool continuous);
     abstract void stop();
diff --git a/src/d6502/cpu.d b/src/d6502/cpu.d
index 97895e5..a8e6356 100644
--- a/src/d6502/cpu.d
+++ b/src/d6502/cpu.d
@@ -60,8 +60,8 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
     }
     final override void run(bool continuous)
     {
-        assert ((memoryRead !is null) && (memoryWrite !is null));
-        assert (tick !is null);
+        assert ((memory.read !is null) && (memory.write !is null));
+        assert (clock.tick !is null);
 
         continueExecution = continuous;
         do
@@ -139,7 +139,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         push(statusByte);
         flag.interrupt = true;
         programCounter = readWord(vector, cast(ushort)(vector + 1));
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
     }
 
     void doReset()
@@ -150,7 +150,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         }
         else
         {
-            tick(); tick();
+            clock.tick(); clock.tick();
         }
 
         peek(STACK_BASE + stackPointer);
@@ -165,35 +165,35 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         signalActive = testSignals();
 
         programCounter = readWord(RESET_VECTOR, RESET_VECTOR + 1);
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
     }
 
     final ubyte read(ushort addr)
     {
         static if (cumulative) ++totalCycles;
-        else tick();
-        return memoryRead(addr);
+        else clock.tick();
+        return memory.read(addr);
     }
 
     final void write(ushort addr, ubyte val)
     {
         static if (cumulative) ++totalCycles;
-        else tick();
-        memoryWrite(addr, val);
+        else clock.tick();
+        memory.write(addr, val);
     }
 
     final void peek(ushort addr)
     {
         static if (cumulative) ++totalCycles;
-        else tick();
-        static if (strict) memoryRead(addr);
+        else clock.tick();
+        static if (strict) memory.read(addr);
     }
 
     final void poke(ushort addr, ubyte val)
     {
         static if (cumulative) ++totalCycles;
-        else tick();
-        static if (strict) memoryWrite(addr, val);
+        else clock.tick();
+        static if (strict) memory.write(addr, val);
     }
 
     final ubyte readFinal(ushort addr)
@@ -461,7 +461,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
     {
         string code = "peek(programCounter);\n";
         code ~= (action == "") ? "" : (action ~ ";");
-        static if (cumulative)  code ~= "tick(totalCycles);\n";
+        static if (cumulative)  code ~= "clock.tick(totalCycles);\n";
         return "override void opcode" ~ opcode ~ "()\n{\n" ~ code ~ "\n}\n";
     }
 
@@ -474,7 +474,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
     {
         string code = "peek(programCounter);\n";
         code ~= UpdateNZ(action);
-        static if (cumulative) code ~= "tick(totalCycles);\n";
+        static if (cumulative) code ~= "clock.tick(totalCycles);\n";
         return "override void opcode" ~ opcode ~ "()\n{\n" ~ code ~ "}\n";
     }
 
@@ -482,7 +482,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
     {
         string code = "readByteOperand();\n" ~
             "if (" ~ action ~ ") addrRelative(cast(byte)operand1);\n";
-        static if (cumulative) code ~= "tick(totalCycles);\n";
+        static if (cumulative) code ~= "clock.tick(totalCycles);\n";
         return "override void opcode" ~ opcode ~ "()\n{\n" ~ code ~ "}\n";
     }
 
@@ -719,7 +719,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         pushWord(programCounter);
 
         finalAddress |= ((operand2 = read(programCounter)) << 8);
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
         programCounter = finalAddress;
     }
 
@@ -729,14 +729,14 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         peek(programCounter);
         flag.fromByte(pull());
         programCounter = readStack() | (readStack() << 8);
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
     }
 
     /* JMP $$$$ */
     final override void opcode4C()
     {
         programCounter = readWordOperand();
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
     }
 
     /* RTS */
@@ -745,7 +745,7 @@ class Cpu(bool strict, bool cumulative)  : CpuBase!(strict, cumulative)
         peek(programCounter);
         programCounter = pullWord();
         peek(programCounter);
-        static if (cumulative) tick(totalCycles);
+        static if (cumulative) clock.tick(totalCycles);
         ++programCounter;
     }
 }
diff --git a/src/system/base.d b/src/system/base.d
index b2ecda4..2e6328a 100644
--- a/src/system/base.d
+++ b/src/system/base.d
@@ -133,10 +133,10 @@ class System
     {
         cpu = newCpu();
         debug(disassemble) cpu.memoryName = &decoder.memoryReadName;
-        cpu.tick = &timer.tick;
+        cpu.clock.tick = &timer.tick;
         timer.onPrimaryStop(&primaryStop);
-        cpu.memoryRead = &decoder.read;
-        cpu.memoryWrite = &decoder.write;
+        cpu.memory.read = &decoder.read;
+        cpu.memory.write = &decoder.write;
     }
 
     void initIO(ubyte[] vidRom)
diff --git a/test/cpu.d b/test/cpu.d
index 796c446..85f5bbd 100644
--- a/test/cpu.d
+++ b/test/cpu.d
@@ -80,9 +80,9 @@ if (isCpu!T)
     else
         void tick() {}
 
-    cpu.memoryRead = &mem.read;
-    cpu.memoryWrite = &mem.write;
-    cpu.tick = &tick;
+    cpu.memory.read = &mem.read;
+    cpu.memory.write = &mem.write;
+    cpu.clock.tick = &tick;
 }
 
 
@@ -99,7 +99,7 @@ auto recordCycles(T)(T cpu)
 if (isCpu!T)
 {
     auto cycles = new int;
-    auto wrappedTick = cpu.tick;
+    auto wrappedTick = cpu.clock.tick;
 
     static if (isCumulative!T)
     {
@@ -117,7 +117,7 @@ if (isCpu!T)
             wrappedTick();
         }
     }
-    cpu.tick = &tick;
+    cpu.clock.tick = &tick;
 
     return constRef(cycles);
 }
@@ -155,9 +155,9 @@ if (isCpu!T)
     auto record = new Bus[actions];
     int c;
 
-    enforce(cpu.memoryRead !is null && cpu.memoryWrite !is null);
-    auto wrappedRead = cpu.memoryRead;
-    auto wrappedWrite = cpu.memoryWrite;
+    enforce(cpu.memory.read !is null && cpu.memory.write !is null);
+    auto wrappedRead = cpu.memory.read;
+    auto wrappedWrite = cpu.memory.write;
 
     ubyte read(ushort addr)
     {
@@ -177,8 +177,8 @@ if (isCpu!T)
         wrappedWrite(addr, val);
     }
 
-    cpu.memoryRead = &read;
-    cpu.memoryWrite = &write;
+    cpu.memory.read = &read;
+    cpu.memory.write = &write;
 
     return record;
 }
@@ -210,8 +210,8 @@ enum Action : ushort { NONE, READ, WRITE }
 void runUntilBRK(T)(T cpu)
 if (isCpu!T)
 {
-    assert(cpu.memoryRead !is null);
-    auto wrappedRead = cpu.memoryRead;
+    assert(cpu.memory.read !is null);
+    auto wrappedRead = cpu.memory.read;
 
     ubyte read(ushort addr)
     {
@@ -219,7 +219,7 @@ if (isCpu!T)
         return wrappedRead(addr);
     }
 
-    cpu.memoryRead = &read;
+    cpu.memory.read = &read;
 
     try { cpu.run(true); } catch (StopException e) {}
 }