Added Brick.reset_motor_position

lib/lego_nxt/brick.rb

@@ -19,6 +19,7 @@ def initialize connection
     #
     # @param [Integer] frequency Range: 200-1400Hz
     # @param [Integer] duration in milliseconds (1/1000 of a second)
+    # @return [nil]
     def play_tone frequency, duration
       raise ArgumentError.new("Frequency must be between 200-1400Hz; got #{frequency}") if frequency < 200 || frequency > 1400
       transmit(
@@ -39,12 +40,27 @@ def battery_level
       ).unpack('S<')[0]
     end
 
+    # Resets the tracking for the motor position.
+    #
+    # @param [Symbol] port The port the motor is attached to. Should be `:a`, `:b`, or `:c`
+    # @param [Boolean] set_relative Sets the position tracking to relative if true, otherwise absolute if false.
+    # @return [nil]
+    def reset_motor_position port, set_relative
+      transmit(
+        DirectOps::NO_RESPONSE,
+        DirectOps::RESETMOTORPOSITION,
+        normalize_motor_port(port),
+        normalize_boolean(set_relative)
+      )
+    end
+
     # A wrapper around the transmit function for the connection.
     #
     # @param [LegoNXT::Type] bits A list of bytes.
     # @return [nil]
     def transmit *bits
-      connection.transmit(bits.map(&:byte_string).join(""))
+      bitstring = bits.map(&:byte_string).join("")
+      connection.transmit bitstring
     end
 
     # A wrapper around the transceive function for the connection.
@@ -64,5 +80,24 @@ def transceive *bits
       return retval[3..-1]
     end
 
+    # Converts a port symbol into the appropriate byte().
+    #
+    # @param [Symbol] port It should be `:a`, `:b`, or `:c` (which correspond to the markings on the brick)
+    # @return [UnsignedByte] The corresponding byte for the port.
+    def normalize_motor_port port
+      @portmap ||= { a: byte(0),
+                     b: byte(1),
+                     c: byte(2) }
+      raise ArgumentError.new("Motor ports must be #{@portmap.keys.inspect}: got #{port.inspect}") unless @portmap.include? port
+      @portmap[port]
+    end
+
+    # Converts a boolean value into `byte(0)` or `byte(1)`
+    #
+    # @param [Object] bool The value to convert.
+    # @return [UnsignedByte] Returns 0 or 1
+    def normalize_boolean bool
+      bool ? byte(1) : byte(0)
+    end
   end
 end

spec/lib/lego_nxt/brick_spec.rb

@@ -51,6 +51,32 @@
     end
   end
 
+  describe ".normalize_motor_port" do
+    [:a, :b, :c].each do |port|
+      context "with port #{port.inspect}" do
+        it "accepts port #{port.inspect}" do
+          subject.normalize_motor_port port
+        end
+        it "it returns a Type" do
+          subject.normalize_motor_port(port).should be_a_kind_of(LegoNXT::Type)
+        end
+      end
+    end
+
+    it "raises an error if it isn't a port symbol" do
+      expect { subject.normalize_motor_port(:d) }.to raise_error(ArgumentError)
+    end
+  end
+
+  describe ".normalize_boolean" do
+    it "returns byte(1) for true" do
+      subject.normalize_boolean(true).should == byte(1)
+    end
+    it "returns byte(0) for false" do
+      subject.normalize_boolean(false).should == byte(0)
+    end
+  end
+
   describe ".play_tone" do
     it "doesn't accept frequencies under 200" do
       expect { subject.play_tone 199, 400 }.to raise_error(ArgumentError)
@@ -86,4 +112,22 @@
     end
   end
 
+  describe ".reset_motor_position" do
+    [:a, :b, :c].each do |port|
+      [true, false].each do |relative|
+        it "accepts port #{port.inspect}, relative #{relative.inspect}" do
+          subject.reset_motor_position port, relative
+        end
+        it "calls normalize_motor_port" do
+          subject.should_receive(:normalize_motor_port).with(port) { byte(0) }
+          subject.reset_motor_position port, relative
+        end
+        it "calls normalize_boolean" do
+          subject.should_receive(:normalize_boolean).with(relative) { byte(0) }
+          subject.reset_motor_position port, relative
+        end
+      end
+    end
+  end
+
 end