1 files changed, 52 insertions, 0 deletions
diff --git a/basys3/basys3.srcs/ppu_aux.vhd b/basys3/basys3.srcs/ppu_aux.vhd
new file mode 100644
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+++ b/basys3/basys3.srcs/ppu_aux.vhd
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+library ieee;
+library work;
+use ieee.std_logic_1164.all;
+--use ieee.numeric_std.all;
+use work.ppu_consts.all;
+
+entity ppu_aux is port(
+	CLK : in std_logic; -- system clock
+	RESET : in std_logic; -- reset memory
+
+	-- internal memory block (AUX)
+	AUX_WEN : in std_logic; -- VRAM AUX write enable
+	AUX_ADDR : in std_logic_vector(PPU_AUX_ADDR_WIDTH-1 downto 0); -- VRAM AUX address
+	AUX_DATA : in std_logic_vector(PPU_AUX_DATA_WIDTH-1 downto 0); -- VRAM AUX data
+	
+	-- aux outputs
+	BG_SHIFT_X : out std_logic_vector(PPU_POS_H_WIDTH-1 downto 0);
+	BG_SHIFT_Y : out std_logic_vector(PPU_POS_V_WIDTH-1 downto 0);
+	FG_FETCH : out std_logic);
+end ppu_aux;
+
+architecture Behavioral of ppu_aux is
+	component er_ram
+		generic(
+			ADDR_W : natural := PPU_AUX_ADDR_WIDTH; -- ADDR line width
+			DATA_W : natural := PPU_AUX_DATA_WIDTH; -- DATA line width
+			ADDR_LOW : natural := 16#0000#; -- starting address
+			ADDR_RANGE : natural := 16#0002#); -- amount of valid addresses after ADDR_LOW
+		port(
+			CLK : in std_logic; -- clock
+			RST : in std_logic; -- async memory clear
+			WEN : in std_logic; -- write enable
+			ADDR : in std_logic_vector(ADDR_W-1 downto 0);
+			DATA : in std_logic_vector(DATA_W-1 downto 0);
+			REG : out std_logic_vector((ADDR_RANGE*DATA_W)-1 downto 0)); -- exposed register output
+	end component;
+
+	signal INT_REG : std_logic_vector(2 * PPU_AUX_DATA_WIDTH - 1 downto 0);
+begin
+	-- docs/architecture.md#auxiliary-memory
+	FG_FETCH <= INT_REG(17);
+	BG_SHIFT_X <= INT_REG(16 downto 8);
+	BG_SHIFT_Y <= INT_REG(7 downto 0);
+
+	RAM : component er_ram port map(
+		CLK => CLK,
+		RST => RESET,
+		WEN => AUX_WEN,
+		ADDR => AUX_ADDR,
+		DATA => AUX_DATA,
+		REG => INT_REG);
+end Behavioral;