学步园

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;