Revert "Revert "Fixing Issue #3: side register handling for floppy co…

…ntroller.""

This reverts commit 413267e.

src/vhdl/bitplane.vhdl

@@ -31,6 +31,8 @@ entity bitplane is
     ----------------------------------------------------------------------
     pixelclock : in  STD_LOGIC;
 
+    reset : in std_logic;
+
     advance_pixel : in std_logic;
     sixteen_colour_mode : in std_logic;
 
@@ -58,6 +60,14 @@ architecture behavioural of bitplane is
 begin
 
   process (pixelclock)
+    variable v_bb_valid_h : std_logic := '0';
+    variable v_bb_valid_2 : std_logic := '0';
+    variable v_bb_valid_3 : std_logic := '0';
+    variable v_byte_bits_available : integer range 0 to 8 := 0;
+    variable v_byte_buffer_head : std_logic_vector(7 downto 0);
+    variable v_byte_buffer_2 : std_logic_vector(7 downto 0);
+    variable v_byte_buffer_3 : std_logic_vector(7 downto 0);
+
   begin
     if pixelclock'event and pixelclock = '1' then
 
@@ -66,58 +76,91 @@ begin
       -- pixels are required on successive clocks.  This keeps the logic
       -- somewhat simpler.
 
+      if reset='1' then
+          bb_valid_h <= '0';
+          bb_valid_2 <= '0';
+          bb_valid_3 <= '0';
+      else
+
       -- Request more data if our buffer is not full.
-      if (bb_valid_h='0' or bb_valid_2='0' or bb_valid_3='0')
-        and (data_in_valid='0') then
+      if (bb_valid_h='0' or bb_valid_2='0' or bb_valid_3='0') then
         data_request <= '1';
       else
         data_request <= '0';
       end if;
 
+      v_bb_valid_h := bb_valid_h;
+      v_bb_valid_2 := bb_valid_2;
+      v_bb_valid_3 := bb_valid_3;
+      v_byte_bits_available := byte_bits_available;
+      v_byte_buffer_head := byte_buffer_head;
+      v_byte_buffer_2 := byte_buffer_2;
+      v_byte_buffer_3 := byte_buffer_3;
+
       -- Accept new data if available
       if data_in_valid='1' then
-        byte_buffer_3 <= std_logic_vector(data_in);
-        bb_valid_3 <= '1';
+          if bb_valid_h='0' then
+              v_byte_buffer_head := std_logic_vector(data_in);
+              v_bb_valid_h := '1';
+              v_byte_bits_available := 8;
+          elsif bb_valid_2='0' then
+              v_byte_buffer_2 := std_logic_vector(data_in);
+              v_bb_valid_2 := '1';
+          elsif bb_valid_3='0' then
+              v_byte_buffer_3 := std_logic_vector(data_in);
+              v_bb_valid_3 := '1';
+          end if;        
       end if;
 
-      -- Shuffle buffer down as required
-      if bb_valid_h='0' and bb_valid_2='1' then
-        byte_buffer_head <= byte_buffer_2;
-        byte_bits_available <= 8;
-        bb_valid_h <= '1';
-        if bb_valid_3='1' then
-          byte_buffer_head <= byte_buffer_2;
-          bb_valid_2 <= '1';
-          bb_valid_3 <= '0';
-        else
-          bb_valid_2 <= '0';
-        end if;
-      end if;
-
-      -- Supply pixels as required
       if advance_pixel='1' then
         if sixteen_colour_mode='0' then
-          byte_bits_available <= byte_bits_available - 1;
-          byte_buffer_head(7 downto 1) <= byte_buffer_head(6 downto 0);
-          byte_buffer_head(0) <= '0';
-          pixel_out <= byte_buffer_head(7);
-          if byte_bits_available = 1 then
-            -- We are using the last bit, so mark byte as empty.
-            bb_valid_h <= '0';
+            if v_byte_bits_available > 0 then   
+	      v_byte_bits_available := v_byte_bits_available - 1;
+	      pixel_out <= v_byte_buffer_head(7);
+	      v_byte_buffer_head(7 downto 1) := v_byte_buffer_head(6 downto 0);
+	      v_byte_buffer_head(0) := '0';
+	      --pixel_out <= '1';
+	      if v_byte_bits_available = 0 then
+	        -- We are using the last bit, so mark byte as empty.
+	        v_bb_valid_h := '0';
+	        if v_bb_valid_2='1' then
+	          -- Shuffle buffer down as required
+		  v_byte_buffer_head := byte_buffer_2;
+	  	  v_byte_bits_available := 8;
+		  v_bb_valid_h := '1';
+		  if v_bb_valid_3='1' then
+		    v_byte_buffer_2 := byte_buffer_3;
+		    v_bb_valid_2 := '1';
+		    v_bb_valid_3 := '0';
+		  else
+		    v_bb_valid_2 := '0';
+		  end if;
+	      end if;
+            end if;
           end if;
         else
-          byte_bits_available <= byte_bits_available - 4;
-          byte_buffer_head(7 downto 4) <= byte_buffer_head(3 downto 0);
-          byte_buffer_head(3 downto 0) <= x"0";
-          if byte_bits_available < 4 then
+          v_byte_bits_available := v_byte_bits_available - 4;
+          v_byte_buffer_head(7 downto 4) := v_byte_buffer_head(3 downto 0);
+          v_byte_buffer_head(3 downto 0) := x"0";
+          if v_byte_bits_available < 4 then
             -- We are using the last bit, so mark byte as empty.
-            bb_valid_h <= '0';
+            v_bb_valid_h := '0';
           end if;
-          pixel16_out <= unsigned(byte_buffer_head(7 downto 4));
+          pixel16_out <= unsigned(v_byte_buffer_head(7 downto 4));
         end if;
+
+      end if;
+      bb_valid_h <= v_bb_valid_h;
+      bb_valid_2 <= v_bb_valid_2;
+      bb_valid_3 <= v_bb_valid_3;
+      byte_bits_available <= v_byte_bits_available;
+      byte_buffer_head <= v_byte_buffer_head;
+      byte_buffer_2 <= v_byte_buffer_2;
+      byte_buffer_3 <= v_byte_buffer_3;
       end if;
 
     end if;
+
   end process;
 
 end behavioural;