Merge branch 'dev' into ppu-interface

1 files changed, 46 insertions, 0 deletions

diff --git a/basys3/basys3.srcs/ppu_pceg.vhd b/basys3/basys3.srcs/ppu_pceg.vhd
new file mode 100644
index 0000000..1aaeee4
--- /dev/null
+++ b/basys3/basys3.srcs/ppu_pceg.vhd
@@ -0,0 +1,46 @@
+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;