with Interfaces;                   use Interfaces;
with AVR;                          use AVR;
with AVR.MCU;
with AVR.Interrupts;
with AVR.Timer0;
with AVR.Wait;

package body Walking_LED is

   --
   --  constant definitions
   --
   XTAL        : constant := 12_000_000;  -- Crystal frequency in Hz
   Timer_Clock : constant :=         2;  -- LED flashing frequency in 1Hz

   Count_Cmp   : constant := XTAL / 1024 / 256 / Timer_Clock - 1;


   --
   -- use volatile if variable is accessed from interrupts and in the
   -- main program.  No volatile if accessed in interrupt only.
   LED : Unsigned_8;

   Count : Unsigned_8;


   procedure Sig_Compare;
   pragma Machine_Attribute (Entity         => SIG_Compare,
                             Attribute_Name => "signal");
   pragma Export (C, Sig_Compare, Timer0.Signal_Compare);

   procedure Wait_1ms is new
     AVR.Wait.Generic_Wait_Usecs(Crystal_Hertz=>8_000_000,
                                 Micro_Seconds=>1000);
   
   procedure Wait_Long is 
   begin
      --delay 0.8;
      for J in 1..80 loop
           Wait_1ms;
      end loop;
   end Wait_Long;
   
   procedure Sig_Compare is
   begin
      Count := Count + 1;

      if Count > Count_Cmp then
         -- invert the output since a zero means: LED on
         MCU.PORTA := not LED;

         -- move to next LED
         LED := Rotate_Left (LED, 1);

         Count := 0;
      end if;
   end Sig_Compare;


   procedure Main is
   begin
      -- use all pins on PortB for output
      MCU.DDRA_Bits := (others => DD_Output);
      -- and turn off all LEDs
      MCU.PORTA := 16#FE#;
      
      for I in 1..8 loop 
         Wait_Long;
         MCU.PORTA:=Rotate_Left(MCU.PORTA,1);
      end loop;
      
      -- use CLK/1024 prescale value, clear timer/counter on compareA match
      Timer0.Init_CTC (Prescaler => Timer0.Scale_By_1024);

      -- enable Output Compare 1 overflow interrupt
      Timer0.Enable_Interrupt_Compare;

      -- init variable representing the LED state
      LED := 1;

      -- generally enable interrupts
      AVR.Interrupts.Enable;

      -- loop forever
      loop null; end loop;
   end Main;

end Walking_Led;