diff --git a/lib/arm/compare_instruction.rb b/lib/arm/compare_instruction.rb
index 0ffd86b8..543592d4 100644
--- a/lib/arm/compare_instruction.rb
+++ b/lib/arm/compare_instruction.rb
@@ -2,22 +2,22 @@ module Arm
   class CompareInstruction < Vm::CompareInstruction
     include Arm::Constants
 
-    def initialize(first , attributes)
-      super(first , attributes) 
+    def initialize(left , right , attributes)
+      super(left , right,  attributes) 
       @attributes[:condition_code] = :al if @attributes[:condition_code] == nil
       @operand = 0
       @i = 0      
       @attributes[:update_status] = 1
-      @rn = first
+      @rn = left
       @rd = :r0
     end
-    # arm intrucioons are pretty sensible, and always 4 bytes (thumb not supported)
+    # arm instructions are pretty sensible, and always 4 bytes (thumb not supported)
     def length
       4
     end
 
     def build 
-      arg = @attributes[:right]
+      arg = @right
 
       if arg.is_a?(Vm::StringConstant)
         # do pc relative addressing with the difference to the instuction
diff --git a/lib/vm/c_machine.rb b/lib/vm/c_machine.rb
index dd2017be..5871d695 100644
--- a/lib/vm/c_machine.rb
+++ b/lib/vm/c_machine.rb
@@ -45,28 +45,28 @@ module Vm
     # Derived machines may use own instructions and define functions for them if so desired
     def initialize
       [:push, :pop].each do |inst|
-        define_instruction_for(inst , StackInstruction)
+        define_instruction_one(inst , StackInstruction)
       end
       [:adc, :add, :and, :bic, :eor, :orr, :rsb, :rsc, :sbc, :sub].each do |inst|
-        define_instruction_for(inst , LogicInstruction)
+        define_instruction_one(inst , LogicInstruction)
       end
       [:mov, :mvn].each do |inst|
-        define_instruction_for(inst , MoveInstruction)
+        define_instruction_one(inst , MoveInstruction)
       end
       [:cmn, :cmp, :teq, :tst].each do |inst|
-        define_instruction_for(inst , CompareInstruction)
+        define_instruction_two(inst , CompareInstruction)
       end
       [:strb, :str , :ldrb, :ldr].each do |inst|
-        define_instruction_for(inst , MemoryInstruction)
+        define_instruction_one(inst , MemoryInstruction)
       end
       [:b, :call , :swi].each do |inst|
-        define_instruction_for(inst , CallInstruction)
+        define_instruction_one(inst , CallInstruction)
       end
       # create all possible brach instructions, but the CallInstruction demangles the 
       # code, and has opcode set to :b and :condition_code set to the condition
       CONDITIONS.each do |suffix|
-        define_instruction_for("b#{suffix}".to_sym , CallInstruction)
-        define_instruction_for("call#{suffix}".to_sym , CallInstruction)
+        define_instruction_one("b#{suffix}".to_sym , CallInstruction)
+        define_instruction_one("call#{suffix}".to_sym , CallInstruction)
       end
     end
 
@@ -74,20 +74,6 @@ module Vm
         self.class.send(:define_method, name , &block)
     end
 
-    # define the instruction inst (given as a symbol) on this class as a methods
-    # As we define a standard set of instructions (or memnonics) , this turns this class into a kind of
-    # Assembler, in that you can write .mov() or .pop() and those functions mean the same as if they 
-    # were in an assembler file (also options are the same)
-    # defaults gets merged into the instructions options hash, ie passed on to the (machine specific)
-    # Instruction constructor and as such can be used to influence that classes behaviour
-    def define_instruction(inst , clazz , defaults = {} )
-      create_method(inst) do |first , options|
-        options = {} if options == nil
-        options.merge defaults
-        options[:opcode] = inst
-        clazz.new(first , options)
-      end
-    end
 
     def self.instance
       @@instance
@@ -105,7 +91,28 @@ module Vm
     #    be used to define the mov on an arm machine. 
     # This methods picks up that derived class and calls a define_instruction methods that can 
     #   be overriden in subclasses 
-    def define_instruction_for(inst , clazz )
+    def define_instruction_one(inst , clazz ,  defaults = {} )
+      clazz =  class_for(clazz)
+      create_method(inst) do |first , options = nil|
+        options = {} if options == nil
+        options.merge defaults
+        options[:opcode] = inst
+        clazz.new(first , options)
+      end
+    end
+
+    # same for two args (left right, from to etc)
+    def define_instruction_two(inst , clazz ,  defaults = {} )
+      clazz =  class_for(clazz)
+      create_method(inst) do |first ,second , options = nil|
+        options = {} if options == nil
+        options.merge defaults
+        options[:opcode] = inst
+        clazz.new(first , second ,options)
+      end
+    end
+
+    def class_for clazz
       c_name = clazz.name
       my_module = self.class.name.split("::").first
       clazz_name = clazz.name.split("::").last
@@ -113,7 +120,7 @@ module Vm
         module_class = eval("#{my_module}::#{clazz_name}") rescue nil
         clazz = module_class if module_class
       end
-      define_instruction(inst , clazz )
+      clazz
     end
   end
 end
diff --git a/lib/vm/instruction.rb b/lib/vm/instruction.rb
index 7ad50ffc..98338f69 100644
--- a/lib/vm/instruction.rb
+++ b/lib/vm/instruction.rb
@@ -55,8 +55,9 @@ module Vm
     end
   end
   class CompareInstruction < Instruction
-    def initialize first , options
-      @first = first
+    def initialize left , right , options
+      @left = left
+      @right = right
       super(options)
     end
   end
diff --git a/test/arm/test_all.rb b/test/arm/test_all.rb
index f086bd4a..f6575565 100644
--- a/test/arm/test_all.rb
+++ b/test/arm/test_all.rb
@@ -2,3 +2,4 @@ require_relative "test_arm"
 require_relative "test_logic"
 require_relative "test_move"
 require_relative "test_memory"
+require_relative "test_compare"
diff --git a/test/arm/test_arm.rb b/test/arm/test_arm.rb
index 24c1fc6b..b1aeb09c 100644
--- a/test/arm/test_arm.rb
+++ b/test/arm/test_arm.rb
@@ -18,14 +18,6 @@ class TestArmAsm < MiniTest::Test
     code = @machine.bic	 :r2 , left: :r2 , right: :r3
     assert_code code , :bic , [0x03,0x20,0xc2,0xe1] #e3 c2 20 44
   end
-  def test_cmn
-    code = @machine.cmn	 :r1 , right: :r2
-    assert_code code , :cmn , [0x02,0x00,0x71,0xe1] #e1 71 00 02
-  end
-  def test_cmp
-    code = @machine.cmp	 :r1 , right: :r2
-    assert_code code , :cmp , [0x02,0x00,0x51,0xe1] #e1 51 00 02
-  end
   def test_push
     code = @machine.push [:lr] , {}
     assert_code code , :push ,  [0x00,0x40,0x2d,0xe9] #e9 2d 40 00
@@ -47,15 +39,7 @@ class TestArmAsm < MiniTest::Test
     assert_code code , :sbc , [0x05,0x30,0xc4,0xe0]#e0 c4 30 05
   end
   def test_swi
-    code = @machine.swi	 0x05 , {}
+    code = @machine.swi	 0x05 
     assert_code code , :swi , [0x05,0x00,0x00,0xef]#ef 00 00 05
   end
-  def test_teq
-    code = @machine.teq  :r1 , right: :r2
-    assert_code code , :teq , [0x02,0x00,0x31,0xe1] #e1 31 00 02
-  end
-  def test_tst
-    code = @machine.tst  :r1 , right: :r2
-    assert_code code , :tst , [0x02,0x00,0x11,0xe1] #e1 11 00 02
-  end
 end
diff --git a/test/arm/test_compare.rb b/test/arm/test_compare.rb
new file mode 100644
index 00000000..9103da47
--- /dev/null
+++ b/test/arm/test_compare.rb
@@ -0,0 +1,22 @@
+require_relative 'helper'
+
+class TestArmAsm < MiniTest::Test
+  include ArmHelper
+
+  def test_cmn
+    code = @machine.cmn	 :r1 , :r2
+    assert_code code , :cmn , [0x02,0x00,0x71,0xe1] #e1 71 00 02
+  end
+  def test_cmp
+    code = @machine.cmp	 :r1 , :r2
+    assert_code code , :cmp , [0x02,0x00,0x51,0xe1] #e1 51 00 02
+  end
+  def test_teq
+    code = @machine.teq  :r1 , :r2
+    assert_code code , :teq , [0x02,0x00,0x31,0xe1] #e1 31 00 02
+  end
+  def test_tst
+    code = @machine.tst  :r1 , :r2 
+    assert_code code , :tst , [0x02,0x00,0x11,0xe1] #e1 11 00 02
+  end
+end
\ No newline at end of file