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---------------------------------------------------------------------
----                                                             ----
----  WISHBONE revB2 compl. I2C Master Core; bit-controller      ----
----                                                             ----
----                                                             ----
----  Author: Richard Herveille                                  ----
----          richard@asics.ws                                   ----
----          www.asics.ws                                       ----
----                                                             ----
----  Downloaded from: http://www.opencores.org/projects/i2c/    ----
----                                                             ----
---------------------------------------------------------------------
----                                                             ----
---- Copyright (C) 2000 Richard Herveille                        ----
----                    richard@asics.ws                         ----
----                                                             ----
---- This source file may be used and distributed without        ----
---- restriction provided that this copyright statement is not   ----
---- removed from the file and that any derivative work contains ----
---- the original copyright notice and the associated disclaimer.----
----                                                             ----
----     THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     ----
---- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   ----
---- TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   ----
---- FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      ----
---- OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,         ----
---- INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES    ----
---- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE   ----
---- GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR        ----
---- BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  ----
---- LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT  ----
---- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT  ----
---- OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE         ----
---- POSSIBILITY OF SUCH DAMAGE.                                 ----
----                                                             ----
---------------------------------------------------------------------
 
--  CVS Log
--
--  $Id: i2c_master_bit_ctrl.vhd,v 1.2 2002-06-15 07:37:04 rherveille Exp $
--
--  $Date: 2002-06-15 07:37:04 $
--  $Revision: 1.2 $
--  $Author: rherveille $
--  $Locker:  $
--  $State: Exp $
--
-- Change History:
--               $Log: not supported by cvs2svn $
--               Revision 1.1  2001/11/05 12:02:33  rherveille
--               Split i2c_master_core.vhd into separate files for each entity; same layout as verilog version.
--               Code updated, is now up-to-date to doc. rev.0.4.
--               Added headers.
--
 
 
--
-------------------------------------
-- Bit controller section
------------------------------------
--
-- Translate simple commands into SCL/SDA transitions
-- Each command has 5 states, A/B/C/D/idle
--
-- start:	SCL	~~~~~~~~~~\____
--	SDA	~~~~~~~~\______
--		 x | A | B | C | D | i
--
-- repstart	SCL	____/~~~~\___
--	SDA	__/~~~\______
--		 x | A | B | C | D | i
--
-- stop	SCL	____/~~~~~~~~
--	SDA	==\____/~~~~~
--		 x | A | B | C | D | i
--
--- write	SCL	____/~~~~\____
--	SDA	==X=========X=
--		 x | A | B | C | D | i
--
--- read	SCL	____/~~~~\____
--	SDA	XXXX=====XXXX
--		 x | A | B | C | D | i
--
 
-- Timing:		Normal mode	Fast mode
-----------------------------------------------------------------
-- Fscl		100KHz		400KHz
-- Th_scl		4.0us		0.6us	High period of SCL
-- Tl_scl		4.7us		1.3us	Low period of SCL
-- Tsu:sta		4.7us		0.6us	setup time for a repeated start condition
-- Tsu:sto		4.0us		0.6us	setup time for a stop conditon
-- Tbuf		4.7us		1.3us	Bus free time between a stop and start condition
--
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
 
entity i2c_master_bit_ctrl is
	generic(
		Tcq : time := 1 ns
	);
	port (
		clk    : in std_logic;
		rst    : in std_logic;
		nReset : in std_logic;
		ena    : in std_logic;				-- core enable signal
 
		clk_cnt : in unsigned(15 downto 0);		-- clock prescale value
 
		cmd     : in std_logic_vector(3 downto 0);
		cmd_ack : out std_logic;
		busy    : out std_logic;
 
		din  : in std_logic;
		dout : out std_logic;
 
		-- i2c lines
		scl_i   : in std_logic;  -- i2c clock line input
		scl_o   : out std_logic; -- i2c clock line output
		scl_oen : out std_logic; -- i2c clock line output enable, active low
		sda_i   : in std_logic;  -- i2c data line input
		sda_o   : out std_logic; -- i2c data line output
		sda_oen : out std_logic  -- i2c data line output enable, active low
	);
end entity i2c_master_bit_ctrl;
 
architecture structural of i2c_master_bit_ctrl is
	constant I2C_CMD_NOP    : std_logic_vector(3 downto 0) := "0000";
	constant I2C_CMD_START  : std_logic_vector(3 downto 0) := "0001";
	constant I2C_CMD_STOP   : std_logic_vector(3 downto 0) := "0010";
	constant I2C_CMD_READ   : std_logic_vector(3 downto 0) := "0100";
	constant I2C_CMD_WRITE  : std_logic_vector(3 downto 0) := "1000";
 
	type states is (idle, start_a, start_b, start_c, start_d, stop_a, stop_b, stop_c, rd_a, rd_b, rd_c, rd_d, wr_a, wr_b, wr_c, wr_d);
	signal c_state : states;
 
	signal iscl_oen, isda_oen : std_logic;          -- internal I2C lines
	signal sSCL, sSDA         : std_logic;          -- synchronized SCL and SDA inputs
	signal dscl_oen           : std_logic;          -- delayed scl_oen signals
 
	signal clk_en, slave_wait :std_logic;           -- clock generation signals
--	signal cnt : unsigned(15 downto 0) := clk_cnt;  -- clock divider counter (simulation)
	signal cnt : unsigned(15 downto 0);             -- clock divider counter (synthesis)
 
begin
	-- synchronize SCL and SDA inputs
	synch_scl_sda: process(clk)
	begin
		if (clk'event and clk = '1') then
			sSCL <= scl_i after Tcq;
			sSDA <= sda_i after Tcq;
		end if;
	end process synch_SCL_SDA;
 
	-- delay scl_oen
	process (clk)
	begin
		if (clk'event and clk = '1') then
			dscl_oen <= iscl_oen after Tcq;
		end if;
	end process;
 
	-- whenever the slave is not ready it can delay the cycle by pulling SCL low
	slave_wait <= dscl_oen and not sSCL;
 
	-- generate clk enable signal
	gen_clken: process(clk, nReset)
	begin
		if (nReset = '0') then
			cnt    <= (others => '0') after Tcq;
			clk_en <= '1' after Tcq;
		elsif (clk'event and clk = '1') then
			if (rst = '1') then
				cnt    <= (others => '0') after Tcq;
				clk_en <= '1' after Tcq;
			else
				if ( (cnt = 0) or (ena = '0') ) then
					clk_en <= '1' after Tcq;
					cnt    <= clk_cnt after Tcq;
				else
					if (slave_wait = '0') then
						cnt <= cnt -1 after Tcq;
					end if;
					clk_en <= '0' after Tcq;
				end if;
			end if;
		end if;
	end process gen_clken;
 
 
	-- generate bus status controller
	bus_status_ctrl: block
		signal dSDA : std_logic;
		signal sta_condition : std_logic;
		signal sto_condition : std_logic;
 
		signal ibusy : std_logic;
	begin
		-- detect start condition => detect falling edge on SDA while SCL is high
		-- detect stop condition  => detect rising edge on SDA while SCL is high
		detect_sta_sto: process(clk)
		begin
			if (clk'event and clk = '1') then
				dSDA <= sSDA;	-- generate a delayed version of sSDA
 
				sta_condition <= (not sSDA and dSDA) and sSCL;
				sto_condition <= (sSDA and not dSDA) and sSCL;
			end if;
		end process detect_sta_sto;
 
		-- generate bus busy signal
		gen_busy: process(clk, nReset)
		begin
			if (nReset = '0') then
				ibusy <= '0' after Tcq;
			elsif (clk'event and clk = '1') then
				if (rst = '1') then
					ibusy <= '0' after Tcq;
				else
					ibusy <= (sta_condition or ibusy) and not sto_condition after Tcq;
				end if;
			end if;
		end process gen_busy;
 
		-- assign output
		busy <= ibusy;
	end block bus_status_ctrl;
 
 
	-- generate statemachine
	nxt_state_decoder : process (clk, nReset, c_state, cmd)
		variable nxt_state : states;
		variable icmd_ack, store_sda : std_logic;
	begin
 
		nxt_state := c_state;
 
		icmd_ack := '0'; -- default no acknowledge
 
		store_sda := '0';
 
		case (c_state) is
			-- idle
			when idle =>
				case cmd is
					when I2C_CMD_START =>
						nxt_state := start_a;
 
					when I2C_CMD_STOP =>
						nxt_state := stop_a;
 
					when I2C_CMD_WRITE =>
						nxt_state := wr_a;
 
					when I2C_CMD_READ =>
						nxt_state := rd_a;
 
					when others =>  -- NOP command
						nxt_state := idle;
				end case;
 
			-- start
			when start_a =>
				nxt_state := start_b;
 
			when start_b =>
				nxt_state := start_c;
 
			when start_c =>
				nxt_state := start_d;
 
			when start_d =>
				nxt_state := idle;
				icmd_ack := '1'; -- command completed
 
			-- stop
			when stop_a =>
				nxt_state := stop_b;
 
			when stop_b =>
				nxt_state := stop_c;
 
			when stop_c =>
				nxt_state := idle;
				icmd_ack := '1'; -- command completed
 
			-- read
			when rd_a =>
				nxt_state := rd_b;
 
			when rd_b =>
				nxt_state := rd_c;
 
			when rd_c =>
				nxt_state := rd_d;
				store_sda := '1';
 
			when rd_d =>
				nxt_state := idle;
				icmd_ack := '1'; -- command completed
 
			-- write
			when wr_a =>
				nxt_state := wr_b;
 
			when wr_b =>
				nxt_state := wr_c;
 
			when wr_c =>
				nxt_state := wr_d;
 
			when wr_d =>
				nxt_state := idle;
				icmd_ack := '1'; -- command completed
 
		end case;
 
		-- generate regs
		if (nReset = '0') then
			c_state <= idle after Tcq;
			cmd_ack <= '0' after Tcq;
			Dout    <= '0' after Tcq;
		elsif (clk'event and clk = '1') then
			if (rst = '1') then
				c_state <= idle after Tcq;
				cmd_ack <= '0' after Tcq;
				Dout    <= '0' after Tcq;
			else
				if (clk_en = '1') then
					c_state <= nxt_state after Tcq;
 
					if (store_sda = '1') then
						dout <= sSDA after Tcq;
					end if;
				end if;
 
				cmd_ack <= icmd_ack and clk_en;
			end if;
		end if;
	end process nxt_state_decoder;
 
	--
	-- convert states to SCL and SDA signals
	--
	output_decoder: process (clk, nReset, c_state, iscl_oen, isda_oen, din)
		variable iscl, isda : std_logic;
	begin
		case (c_state) is
			when idle =>
				iscl := iscl_oen; -- keep SCL in same state
				isda := isda_oen; -- keep SDA in same state
 
			-- start
			when start_a =>
				iscl := iscl_oen; -- keep SCL in same state (for repeated start)
				isda := '1';      -- set SDA high
 
			when start_b =>
				iscl := '1';	-- set SCL high
				isda := '1'; -- keep SDA high
 
			when start_c =>
				iscl := '1';	-- keep SCL high
				isda := '0'; -- sel SDA low
 
			when start_d =>
				iscl := '0'; -- set SCL low
				isda := '0'; -- keep SDA low
 
			-- stop
			when stop_a =>
				iscl := '0'; -- keep SCL disabled
				isda := '0'; -- set SDA low
 
			when stop_b =>
				iscl := '1'; -- set SCL high
				isda := '0'; -- keep SDA low
 
			when stop_c =>
				iscl := '1'; -- keep SCL high
				isda := '1'; -- set SDA high
 
			-- write
			when wr_a =>
				iscl := '0';	-- keep SCL low
				isda := din; -- set SDA
 
			when wr_b =>
				iscl := '1';	-- set SCL high
				isda := din; -- keep SDA
 
			when wr_c =>
				iscl := '1';	-- keep SCL high
				isda := din; -- keep SDA
 
			when wr_d =>
				iscl := '0'; -- set SCL low
				isda := din; -- keep SDA
 
			-- read
			when rd_a =>
				iscl := '0'; -- keep SCL low
				isda := '1'; -- tri-state SDA
 
			when rd_b =>
				iscl := '1'; -- set SCL high
				isda := '1'; -- tri-state SDA
 
			when rd_c =>
				iscl := '1'; -- keep SCL high
				isda := '1'; -- tri-state SDA
 
			when rd_d =>
				iscl := '0'; -- set SCL low
				isda := '1'; -- tri-state SDA
		end case;
 
		-- generate registers
		if (nReset = '0') then
			iscl_oen <= '1' after Tcq;
			isda_oen <= '1' after Tcq;
		elsif (clk'event and clk = '1') then
			if (rst = '1') then
				iscl_oen <= '1' after Tcq;
				isda_oen <= '1' after Tcq;
			else
				if (clk_en = '1') then
					iscl_oen <= iscl after Tcq;
					isda_oen <= isda after Tcq;
				end if;
			end if;
		end if;
	end process output_decoder;
 
	-- assign outputs
	scl_o   <= '0';
	scl_oen <= iscl_oen;
	sda_o   <= '0';
	sda_oen <= isda_oen;
end architecture structural;