mirror of
https://github.com/MiSTer-devel/Gameboy_MiSTer.git
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4f937979ec
Maximum of 6 extra sprites per line Extra sprites are fetched during mode2 to not break mode3 timing
100 lines
2.2 KiB
VHDL
100 lines
2.2 KiB
VHDL
library IEEE;
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use IEEE.std_logic_1164.all;
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use IEEE.numeric_std.all;
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entity speedcontrol is
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port
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(
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clk_sys : in std_logic;
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reset : in std_logic;
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romread : in std_logic;
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romack : in std_logic;
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pausevideo : in std_logic;
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ce : out std_logic := '0';
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ce_n : out std_logic := '0';
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ce_2x : out std_logic := '0'
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);
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end entity;
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architecture arch of speedcontrol is
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signal clkdiv : unsigned(2 downto 0) := (others => '0');
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type tstate is
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(
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NORMAL,
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WAITRAM
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);
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signal state : tstate := NORMAL;
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begin
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process(clk_sys)
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variable skipclock : std_logic;
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begin
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if falling_edge(clk_sys) then
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ce <= '0';
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ce_n <= '0';
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ce_2x <= '0';
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skipclock := '0';
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clkdiv <= clkdiv + 1;
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if (clkdiv = "000") then
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ce <= '1';
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end if;
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if (clkdiv = "100") then
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ce_n <= '1';
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end if;
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if (clkdiv(1 downto 0) = "00") then
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ce_2x <= '1';
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end if;
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if (reset = '1') then
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state <= NORMAL;
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else
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case (state) is
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when NORMAL =>
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if (romread = '1') then
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state <= WAITRAM;
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end if;
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when WAITRAM =>
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if (romack = '1') then
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state <= NORMAL;
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else
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skipclock := '1';
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end if;
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end case;
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end if;
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if (pausevideo = '1') then
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skipclock := '1';
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end if;
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if (skipclock = '1') then
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ce <= '0';
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ce_n <= '0';
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ce_2x <= '0';
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if (clkdiv = "100") then
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clkdiv <= "001";
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end if;
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if (clkdiv = "000") then
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clkdiv <= "101";
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end if;
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end if;
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end if;
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end process;
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end architecture;
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