library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity sdram_ctrl is
port
(	
	clock_100	:	in std_logic;
	reset_n		:	in std_logic;

	b_cs_n		:	in std_logic;
	b_rd_n		:	in std_logic;
	b_wr_n		:	in std_logic;

	b_wait_n	:	out std_logic;

	b_addr		:	in std_logic_vector(15 downto 0);
	b_data		:	inout std_logic_vector(7 downto 0);


	sdram_clk	:	out std_logic;

	sdram_cs_n	:	out std_logic;
	sdram_cas_n	:	out std_logic;
	sdram_ras_n	:	out std_logic;
	sdram_we_n	:	out std_logic;
	sdram_cke	:	out std_logic;

	sdram_addr	:	out std_logic_vector(12 downto 0);
	sdram_ba	:	out std_logic_vector(1 downto 0);

	sdram_dq	:	inout std_logic_vector(15 downto 0);
	sdram_dqm	:	out std_logic_vector(1 downto 0)
);
end entity;

architecture rtl of sdram_ctrl is

signal clock : std_logic;


signal ack_refresh_request : std_logic;
signal refresh_request : std_logic;
subtype uint13_t is integer range 0 to 8191;
signal refresh_counter : uint13_t;
signal init_done : std_logic;


signal      i_addr : std_logic_vector(12 downto 0);
signal      i_cmd : std_logic_vector(3 downto 0);
subtype uint4_t is integer range 0 to 15;
signal      i_count : uint4_t;
subtype uint3_t is integer range 0 to 7;
signal      i_next : uint3_t;
signal      i_refs : uint3_t;
signal      i_state :uint3_t;

constant I_ST_RESET_WAIT : uint3_t:=0;
constant I_ST_PRECHARGE : uint3_t :=1;
constant I_ST_REFRESH : uint3_t :=2;
constant I_ST_WAIT_COUNT : uint3_t :=3;
constant I_ST_SET_MODE : uint3_t :=4;
constant I_ST_DONE : uint3_t :=5;


-- CS_N RAS_N CAS_N WE_N

constant CMD_IGN : std_logic_vector(3 downto 0 ):="1111";
constant CMD_NOP : std_logic_vector(3 downto 0 ):="0111";
constant CMD_READ : std_logic_vector(3 downto 0 ):="0101";
constant CMD_WRIT : std_logic_vector(3 downto 0 ):="0100";
constant CMD_ACTV : std_logic_vector(3 downto 0 ):="0011";
constant CMD_PRE : std_logic_vector(3 downto 0 ):="0010";
constant CMD_REF : std_logic_vector(3 downto 0 ):="0001";
constant CMD_MRS : std_logic_vector(3 downto 0 ):="0000";

signal m_state : std_logic_vector(8 downto 0);


function active_high(constant val : in boolean) return std_logic is begin
	if val then
		return '1';
	else
		return '0';
	end if;
end function active_high; 


begin

clock<=clock_100;

refresh_counter_process: process(reset_n,clock) begin
	if reset_n = '0' then
		refresh_counter <= 8000;
	elsif rising_edge(clock) then
		if refresh_counter = 0 then
			refresh_counter <= 624;
		else
			refresh_counter <= refresh_counter - 1;	
		end if;
	end if; 
end process;


refresh_request_process: process(reset_n,clock,refresh_counter,refresh_request,init_done,ack_refresh_request) begin
	if reset_n = '0' then
		refresh_request <= '0';
	elsif rising_edge(clock) then
		refresh_request <= (active_high(refresh_counter = 0) or refresh_request) and init_done and not ack_refresh_request;
	end if;
end process;


init_done_process: process (reset_n,clock,i_state)  begin
	if reset_n = '0' then 
		init_done <= '0';
	elsif rising_edge(clock) then
		init_done <= init_done or active_high(i_state = I_ST_DONE );
	end if;
end process;

init_fsm: process (reset_n,clock,i_state,i_count,i_next,refresh_counter) begin
	if reset_n = '0' then
		i_state <= I_ST_RESET_WAIT;
		i_next <= I_ST_RESET_WAIT;
		i_cmd <= CMD_IGN;
		i_addr <= (others => '1');
		i_count <= 0;
	elsif rising_edge(clock) then
	
		if i_state = I_ST_RESET_WAIT then
			-- after reset wait until the refresh_counter ticks over for RAM to stabalize
			i_cmd <= CMD_IGN;
			i_refs <= 0;
			if refresh_counter=0 then
				i_state <= I_ST_PRECHARGE;
			end if;
		elsif i_state = I_ST_PRECHARGE then
			-- precharge all banks, wait one clock, then go to refresh
			i_cmd <=CMD_PRE;
			i_state <= I_ST_WAIT_COUNT;
			i_count <= 1;
			i_next <= I_ST_REFRESH;
		elsif i_state =I_ST_REFRESH then
			-- repeat 7 times { refresh, wait 5 counts }
			i_cmd <=CMD_REF;
			i_refs <= i_refs + 1;

			i_state <= I_ST_WAIT_COUNT;
			i_count <= 5;

			if i_refs = 7 then
				i_next <= I_ST_SET_MODE;
			else
				i_next <= I_ST_REFRESH;
			end if;
		elsif i_state = I_ST_WAIT_COUNT then
			-- wait i_count ticks then goto state i_next
			i_cmd <= CMD_NOP;
			if (i_count > 1) then
				i_count <= i_count -1;
			else
				i_state <= i_next;
			end if;

		elsif i_state=I_ST_SET_MODE then
			-- set mode, wait 3 ticks then goto done
			i_cmd <= CMD_MRS;

			-- reserverd			000
			-- opcode burst read/write	0
			-- reserved 			00
			-- cas latency 3		011
			-- sequential burst		0
			-- burst length 1 		000

			i_addr <= "0000000110000";
			i_count <= 3;
			i_next <= I_ST_DONE;

		elsif i_state=I_ST_DONE then
			i_state <= I_ST_DONE;
		else
			i_state <= I_ST_RESET_WAIT;			
		end if;
	end if;
end process;

main_fsm: process (reset_n,clock,m_state,refresh_counter) begin

end process;

if reset_n ='0' then
m_state <= M_ST_1;
m_next <= M_ST_1;
m_cmd	<= CMD_IGN;
m_bank <= "00";
m_addr <= "0000000000000";
m_data <= "0000000000000000";
m_dqm <= "00";
m_count <= 0;
ack_refresh_request <= 0;
f_pop <= 0;
oe <= 0;
elsif rising_edge(clock) then
if m_state = M_ST_1 then
	if active_high(init_done) then
		if active_high(refresh_request) then
			m_cmd <= CMD_NOP;
		else 
			m_vmd <= CMD_IGN; 
		end if;
		ack_refresh_request <='1';
			
		if active_high(refresh_request) then
			m_state <= M_ST_7;
			m_next <= M_ST_8;
			m_count <= 1;
			active_cs_n <= '1';
		elsif (not active_high(f_empty)) then 
			f_pop <= '1';
			active_cs_n <= f_cs_n;
			active_rnw <= f_rnw;
			active_addr <= f_addr;
			active_data <= f_data;
			m_state <= M_ST_2;
		end if;
	else
		m_addr <= i_addr;
		m_state <= M_ST_1;
		m_next <= M_ST_1;
		m_cmd <= i_cmd;
	end if;
elsif m_state = M_ST_2 then
	m_state <= M_ST_3;
	m_cmd(3) <= csn_decode;
	m_cmd(2 downto 0)="111";
	m_bank <= active_bank;
	m_addr <= active_addr(22 downto 10);
	m_data <= active_data;
	m_dqm <= active_dqm;
	m_count <=2;
	if (active_high(active_rnw)) then
		m_next <=M_ST_4;
	else
		m_next <=M_ST_5;
	end if;
elsif m_state = M_ST_3



end;