---- file: pio_tctrl.vhd--	description: PIO mode timing controller for ATA controller-- author : Richard Herveille-- rev.: 1.0 march  7th, 2001. Initial release-- rev.: 1.1 July  11th, 2001. Changed 'igo' & 'hold_go' signal generation.--------------------------------- PIO Timing controller ----------------------------------- Timing	PIO mode transfers------------------------------------------------ T0:	cycle time-- T1:	address valid to DIOR-/DIOW--- T2:	DIOR-/DIOW- pulse width-- T2i:	DIOR-/DIOW- recovery time-- T3:	DIOW- data setup-- T4:	DIOW- data hold-- T5:	DIOR- data setup-- T6:	DIOR- data hold-- T9:	address hold from DIOR-/DIOW- negated-- Trd:	Read data valid to IORDY asserted-- Ta:	IORDY setup time-- Tb:	IORDY pulse width---- Transfer sequence------------------------------------ 1)	set address (DA, CS0-, CS1-)-- 2)	wait for T1-- 3)	assert DIOR-/DIOW---	   when write action present Data (timing spec. T3 always honored), enable output enable-signal-- 4)	wait for T2-- 5)	check IORDY--	   when not IORDY goto 5-- 	  when IORDY negate DIOW-/DIOR-, latch data (if read action)--    when write, hold data for T4, disable output-enable signal-- 6)	wait end_of_cycle_time. This is T2i or T9 or (T0-T1-T2) whichever takes the longest-- 7)	start new cyclelibrary ieee;use ieee.std_logic_1164.all;use ieee.std_logic_arith.all;library count;use count.count.all;entity PIO_tctrl is	generic(		TWIDTH : natural := 8;                   -- counter width		-- PIO mode 0 settings (@100MHz clock)		PIO_mode0_T1 : natural := 6;             -- 70ns		PIO_mode0_T2 : natural := 28;            -- 290ns		PIO_mode0_T4 : natural := 2;             -- 30ns		PIO_mode0_Teoc : natural := 23           -- 240ns ==> T0 - T1 - T2 = 600 - 70 - 290 = 240	);	port(		clk : in std_logic;                      -- master clock		nReset : in std_logic;                   -- asynchronous active low reset		rst : in std_logic;                      -- synchronous active high reset		-- timing/control register settings		IORDY_en : in std_logic;                 -- use IORDY (or not)		T1 : in unsigned(TWIDTH -1 downto 0);    -- T1 time (in clk-ticks)		T2 : in unsigned(TWIDTH -1 downto 0);    -- T2 time (in clk-ticks)		T4 : in unsigned(TWIDTH -1 downto 0);    -- T4 time (in clk-ticks)		Teoc : in unsigned(TWIDTH -1 downto 0);  -- end of cycle time		-- control signals		go : in std_logic;                       -- PIO controller selected (strobe signal)		we : in std_logic;                       -- write enable signal. '0'=read from device, '1'=write to device		-- return signals		oe :  buffer std_logic;                  -- output enable signal		done : out std_logic;                    -- finished cycle		dstrb : out std_logic;                   -- data strobe, latch data (during read)		-- ATA signals		DIOR,                                    -- IOread signal, active high		DIOW : buffer std_logic;                 -- IOwrite signal, active high		IORDY : in std_logic                     -- IORDY signal	);end entity PIO_tctrl;architecture structural of PIO_tctrl is	component ro_cnt is	generic(SIZE : natural := 8);	port(		clk : in std_logic;                                   -- master clock		nReset : in std_logic := '1';                         -- asynchronous active low reset		rst : in std_logic := '0';                            -- synchronous active high reset		cnt_en : in std_logic := '1';                         -- count enable		go : in std_logic;                                    -- load counter and start sequence		done : out std_logic;                                 -- done counting		D : in unsigned(SIZE -1 downto 0);                    -- load counter value		Q : out unsigned(SIZE -1 downto 0);                   -- current counter value				ID : in unsigned(SIZE -1 downto 0) := (others => '0') -- initial data after reset	);	end component ro_cnt;	-- PIO mode 0 settings (@100MHz clock)	constant T1_m0 : unsigned(TWIDTH -1 downto 0) := conv_unsigned(PIO_mode0_T1, TWIDTH);    -- 70ns	constant T2_m0 : unsigned(TWIDTH -1 downto 0) := conv_unsigned(PIO_mode0_T2, TWIDTH);   -- 290ns	constant T4_m0 : unsigned(TWIDTH -1 downto 0) := conv_unsigned(PIO_mode0_T4, TWIDTH);    -- 30ns	constant Teoc_m0 : unsigned(TWIDTH -1 downto 0) := conv_unsigned(PIO_mode0_Teoc, TWIDTH); -- 240ns ==> T0 - T1 - T2 = 600 - 70 - 290 = 240	signal T1done, T2done, T4done, Teoc_done, IORDY_done : std_logic;	signal busy, hold_go, igo, hT2done : std_logic;begin	-- generate internal go strobe	-- strecht go until ready for new cycle	process(clk, nReset)	begin		if (nReset = '0') then			busy <= '0';			hold_go <= '0';		elsif (clk'event and clk = '1') then			if (rst = '1') then				busy <= '0';				hold_go <= '0';			else				busy <= (igo or busy) and not Teoc_done;				hold_go <= (go or (hold_go and busy)) and not igo;			end if;		end if;	end process;	igo <= (go or hold_go) and not busy;	-- 1)	hookup T1 counter	t1_cnt : ro_cnt generic map (SIZE => TWIDTH)		port map (clk => clk, nReset => nReset, rst => rst, go => igo, D => T1, ID => T1_m0, done => T1done);	-- 2)	set (and reset) DIOR-/DIOW-, set output-enable when writing to device	T2proc: process(clk, nReset)	begin		if (nReset = '0') then			DIOR <= '0';			DIOW <= '0';			oe   <= '0';		elsif (clk'event and clk = '1') then			if (rst = '1') then				DIOR <= '0';				DIOW <= '0';				oe   <= '0';			else				DIOR <= (not we and T1done) or (DIOR and not IORDY_done);				DIOW <= (    we and T1done) or (DIOW and not IORDY_done);				oe   <= ( (we and igo) or oe) and not T4done; -- negate oe when t4-done			end if;		end if;	end process T2proc;	-- 3)	hookup T2 counter	t2_cnt : ro_cnt generic map (SIZE => TWIDTH)		port map (clk => clk, nReset => nReset, rst => rst, go => T1done, D => T2, ID => T2_m0, done => T2done);	-- 4)	check IORDY (if used), generate release_DIOR-/DIOW- signal (ie negate DIOR-/DIOW-)	-- hold T2done	gen_hT2done: process(clk, nReset)	begin		if (nReset = '0') then			hT2done <= '0';		elsif (clk'event and clk = '1') then			if (rst = '1') then				hT2done <= '0';			else				hT2done <= (T2done or hT2done) and not IORDY_done;			end if;		end if;	end process gen_hT2done;	IORDY_done <= (T2done or hT2done) and (IORDY or not IORDY_en);	-- generate datastrobe, capture data at rising DIOR- edge	gen_dstrb: process(clk)	begin		if (clk'event and clk = '1') then			dstrb <= IORDY_done;		end if;	end process gen_dstrb;	-- hookup data hold counter	dhold_cnt : ro_cnt generic map (SIZE => TWIDTH)		port map (clk => clk, nReset => nReset, rst => rst, go => IORDY_done, D => T4, ID => T4_m0, done => T4done);	done <= T4done; -- placing done here provides the fastest return possible,                   -- while still guaranteeing data and address hold-times	-- 5)	hookup end_of_cycle counter	eoc_cnt : ro_cnt generic map (SIZE => TWIDTH)		port map (clk => clk, nReset => nReset, rst => rst, go => IORDY_done, D => Teoc, ID => Teoc_m0, done => Teoc_done);end architecture structural;