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library ieee;
use ieee.std_logic_1164.all;
--use ieee.numeric_std.all;
entity ppu_pceg is port(
CLK : in std_logic; -- system clock
RESET : in std_logic; -- async reset
SPRITE : out std_logic; -- sprite info fetch + sprite pixel fetch
COMP_PAL : out std_logic; -- compositor + palette lookup
DONE : out std_logic); -- last pipeline stage done
end ppu_pceg;
architecture Behavioral of ppu_pceg is
constant PPU_PL_TOTAL_STAGES : natural := 14;
type states is (PL_SPRITE, PL_COMP_PAL, PL_DONE);
signal state : states := PL_SPRITE;
begin
-- output drivers
SPRITE <= CLK when RESET = '0' and state = PL_SPRITE else '0';
COMP_PAL <= CLK when RESET = '0' and state = PL_COMP_PAL else '0';
DONE <= '1' when RESET = '0' and state = PL_DONE else '0';
process(CLK, RESET)
variable CLK_IDX : natural range 0 to PPU_PL_TOTAL_STAGES+1 := 0;
begin
if RESET = '1' then
state <= PL_SPRITE;
elsif rising_edge(CLK) then
-- clock counter ranges
if CLK_IDX < 4 then
state <= PL_SPRITE;
elsif CLK_IDX < 5 then
state <= PL_COMP_PAL;
else
state <= PL_DONE;
end if;
-- increment clock counter
CLK_IDX := CLK_IDX + 1;
if CLK_IDX = PPU_PL_TOTAL_STAGES then
CLK_IDX := 0;
end if;
end if;
end process;
end Behavioral;
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