diff --git a/lib/risc/platform.rb b/lib/risc/platform.rb
index 5b4db22e..6469ea39 100644
--- a/lib/risc/platform.rb
+++ b/lib/risc/platform.rb
@@ -8,17 +8,19 @@ module Risc
     # return the translator instance that traslates risc intructions into
     # platform specific ones
     def translator
-      raise "not implemented"
+      raise "not implemented in #{self.class}"
     end
 
     # return an integer where the binary is loaded
     def loaded_at
-      raise "not implemented"
+      raise "not implemented in #{self.class}"
     end
 
-    # return the number of registers the platform supports
-    def num_registers
-      raise "not implemented"
+    # return an array of register names that should be used by the allocator
+    # does not include :message
+    # could be in interpreter and arm, but here for now
+    def register_names
+      (1 ... 16).collect{|i| "r#{i}".to_sym }
     end
 
     # return the Allocator for the platform
@@ -30,6 +32,19 @@ module Risc
       StandardAllocator.new(compiler , self )
     end
 
+    def assign_reg?(name)
+      case name
+      when :message
+        :r0
+      when :syscall_1
+        :r0
+      when :syscall_2
+        :r1
+      else
+        nil
+      end
+    end
+
     # Factory method to create a Platform object according to the platform
     # string given.
     # Currently only "Arm" and "Interpreter"
diff --git a/lib/risc/standard_allocator.rb b/lib/risc/standard_allocator.rb
index cb8f931f..f3272015 100644
--- a/lib/risc/standard_allocator.rb
+++ b/lib/risc/standard_allocator.rb
@@ -14,7 +14,7 @@ module Risc
       @platform = platform
       @used_regs = {}
       @release_points = Hash.new {|hash , key | hash[key] = [] }
-      @reg_names = (0 ... platform.num_registers).collect{|i| "r#{i}".to_sym }
+      @reg_names = platform.register_names
     end
     attr_reader :used_regs , :compiler , :platform , :reg_names
 
@@ -49,9 +49,11 @@ module Risc
 
     def assign(instruction)
       names = instruction.register_names
-      names.each do |for_name|
-        new_reg = get_reg(for_name)
+      #puts "AT #{instruction}"
+      names.each do |ssa_name|
+        new_reg = get_reg(ssa_name)
         # swap name out
+        #puts "Assign #{new_reg} for #{ssa_name}"
       end
       names
     end
@@ -76,10 +78,6 @@ module Risc
       released
     end
 
-    def used_regs_empty?
-      @used_regs.empty?
-    end
-
     # use the given reg (first) parameter and mark it as assigned to
     # it's ssa form, the second parameter.
     # forward check is trivial, and reverse_used provides reverse check
@@ -88,6 +86,7 @@ module Risc
       raise "Stupid error #{reg}" unless reg.is_a?(Symbol)
       #puts "Using #{reg} for #{ssa_name}"
       @used_regs[reg] = ssa_name
+      reg
     end
 
     # Check whether a register has been assigned to the given ssa form given.
@@ -104,6 +103,12 @@ module Risc
     def get_reg(ssa_name)
       name = reverse_used( ssa_name )
       return name if name
+      get_next_free(ssa_name)
+    end
+
+    def get_next_free(ssa_name)
+      reg = platform.assign_reg?( ssa_name )
+      return use_reg(reg , ssa_name) if reg
       @reg_names.each do |name|
         return use_reg(name , ssa_name) unless @used_regs.has_key?(name)
       end
diff --git a/test/risc/test_platform.rb b/test/risc/test_platform.rb
index eee5291f..6071eb1f 100644
--- a/test/risc/test_platform.rb
+++ b/test/risc/test_platform.rb
@@ -13,8 +13,24 @@ module Risc
       assert_raises{ Platform.for("NotArm")}
     end
     def test_allocate
-      allocator = Platform.new.allocator(FakeCompiler.new)
+      allocator = Platform.for("Interpreter").allocator(FakeCompiler.new)
       assert_equal FakeCompiler , allocator.compiler.class
     end
+    def test_map_message
+      assert_equal :r0 , Platform.new.assign_reg?(:message)
+    end
+    def test_map_sys
+      assert_equal :r0 , Platform.new.assign_reg?(:syscall_1)
+    end
+    def test_map_id
+      assert_nil Platform.new.assign_reg?(:id_some_id)
+    end
+    def test_names_len
+      assert_equal 15 , Platform.new.register_names.length
+    end
+    def test_names_r
+      assert_equal "r" , Platform.new.register_names.first.to_s[0]
+      assert_equal "r" , Platform.new.register_names.last.to_s[0]
+    end
   end
 end
diff --git a/test/risc/test_standard_allocator.rb b/test/risc/test_standard_allocator.rb
index 615821f4..8afeeb05 100644
--- a/test/risc/test_standard_allocator.rb
+++ b/test/risc/test_standard_allocator.rb
@@ -13,11 +13,8 @@ module Risc
     def test_regs
       assert_equal Hash , @allocator.used_regs.class
     end
-    def test_empty
-      assert @allocator.used_regs_empty?
-    end
     def test_reg_names
-      assert_equal 16 , @allocator.reg_names.length
+      assert_equal 15 , @allocator.reg_names.length
     end
     def test_compiler
       assert_equal CallableCompiler , @allocator.compiler.class