command.vhd

标准SDR SDRAM控制器参考设计_verilog_latticesdr_ctrl.v

	-- logic that generates the OE signal for the data path module
	-- For normal burst write he duration of OE is dependent on the configured burst length.
	-- For page mode accesses(SC_PM=1) the OE signal is turned on at the start of the write command
	-- and is left on until a PRECHARGE(page burst terminate) is detected.
	--
	process(CLK, RESET_N)
	begin
		if (RESET_N = '0') then
                oe_shift <= (others => '0');
                oe1      <= '0';
                oe2      <= '0';
                oe3      <= '0';
                oe4      <= '0';
                OE       <= '0';
		elsif rising_edge(CLK) then
                if (SC_PM = '0') then
                        if (do_writea1 = '1') then
                                if (SC_BL = "0001") then                       --  Set the shift register to the appropriate
                                        oe_shift <= (others => '0');                -- value based on burst length.
                                elsif (SC_BL = "0010") then
                                        oe_shift <= "00000001";
                                elsif (SC_BL = "0100") then
                                        oe_shift <= "00000111";
                                elsif (SC_BL = "1000") then
                                        oe_shift <= "01111111";
                                end if;
                                oe1 <= '1';
                        else 
                                oe_shift(6 downto 0) <= oe_shift(7 downto 1);       -- Do the shift operation
                                oe_shift(7)   <= '0';
                                oe1  <= oe_shift(0);
                                oe2  <= oe1;
                                oe3  <= oe2;
                                oe4   <= oe3;
                                if (SC_RC = "10") then
                                        OE <= oe3;
                                else
                                        OE <= oe4;
                                end if;
                        end if;
                else
                        if (do_writea1 = '1') then                                    -- OE generation for page mode accesses
                                oe4   <= '1';
                        elsif (do_precharge = '1' or do_reada = '1' or do_refresh = '1') then
                                oe4   <= '0';
                        end if;
                        OE <= oe4;
                end if;
                               
		end if;
	end process;






	-- This process tracks the time between the activate command and the
	-- subsequent WRITEA or READA command, RC.  The shift register is set using
	-- the configuration register setting SC_RC. The shift register is loaded with
	-- a single '1' with the position within the register dependent on SC_RC.
	-- When the '1' is shifted out of the register it sets so_rw which triggers
	-- a writea or reada command
	--
	process(CLK, RESET_N)
	begin
		if (RESET_N = '0') then
                rw_shift <= (others => '0');
                do_rw    <= '0';
		elsif rising_edge(CLK) then
                if ((do_reada = '1') or (do_writea = '1')) then
                        if (SC_RC = "01") then                                      -- Set the shift register
                                do_rw <= '1';
                        elsif (SC_RC = "10")	then
                                rw_shift <= "0001";
                        elsif (SC_RC = "11")	then
                                rw_shift <= "0010";
                        end if;
                else
                        rw_shift(2 downto 0) 	<= rw_shift(3 downto 1);           -- perform the shift operation
                        rw_shift(3) 			<= '0';
                        do_rw         			<= rw_shift(0);
                end if;
		end if;
	end process;


	
	
	-- This process generates the command acknowledge, CM_ACK, signal.
	-- It also generates the acknowledge signal, REF_ACK, that acknowledges
	-- a refresh request that was generated by the internal refresh timer circuit.
	process(CLK, RESET_N)
	begin
		if (RESET_N = '0') then
                CM_ACK   <= '0';
                REF_ACK  <= '0';
		elsif rising_edge(CLK) then
                if (do_refresh = '1' and REF_REQ = '1') then                        -- Internal refresh timer refresh request
                        REF_ACK <= '1';
                elsif ((do_refresh = '1') or (do_reada = '1') or (do_writea = '1') or (do_precharge = '1')   -- externa  commands
                         or (do_load_mode = '1')) then
                        CM_ACK <= '1';
                else
                        REF_ACK <= '0';
                        CM_ACK  <= '0';
                end if;
		end if;
	end process;






	-- This process generates the address, cs, cke, and command signals(ras,cas,wen)
	--
	process(CLK, RESET_N)
	begin
		if (RESET_N = '0') then
                SA    <= (others => '0');
                BA    <= (others => '0');
                CS_N  <= "01";
                RAS_N <= '1';
                CAS_N <= '1';
                WE_N  <= '1';
                CKE   <= '0';

		elsif rising_edge(CLK) then
                CKE <= '1';
	
	-- Generate SA 			
                if (do_writea = '1' or do_reada = '1') then               -- ACTIVATE command is being issued, so present the row address
                        SA(ROWSIZE-1 downto 0) <= rowaddr;
                else
                        SA(COLSIZE-1 downto 0) <=  coladdr;               -- else alway present column address
                end if;
                if ((do_rw='1') or (do_precharge='1')) then
                        SA(10) <= not(SC_PM);                             -- set SA(10) for autoprecharge read/write or for a precharge all command
                end if;
                                                                          -- don't set it if the controller is in page mode.           	
                if (do_precharge='1' or do_load_mode='1') then
                        BA <= "00";                                       -- Set BA=0 if performing a precharge or load_mode command
                else
                        BA <= bankaddr(1 downto 0);                       -- else set it with the appropriate address bits
                end if;
				
                if (do_refresh='1' or do_precharge='1' or do_load_mode='1') then
                        CS_N <= "00";                                     -- Select both chip selects if performing
                else                                                      -- refresh, precharge(all) or load_mode
                        CS_N(0) <= SADDR(ASIZE-1);                        -- else set the chip selects based off of the
                        CS_N(1) <= not(SADDR(ASIZE-1));                   -- msb address bit
                end	if;
	
	
	--Generate the appropriate logic levels on RAS_N, CAS_N, and WE_N
	--depending on the issued command.
	--				
                if (do_refresh='1') then                        -- Refresh: S=00, RAS=0, CAS=0, WE=1
                        RAS_N <= '0';
                        CAS_N <= '0';
                        WE_N  <= '1';
                elsif ((do_precharge='1') and ((oe4 = '1') or (rw_flag = '1'))) then      -- burst terminate if write is active
                        RAS_N <= '1';
                        CAS_N <= '1';
                        WE_N  <= '0';
                elsif ((do_precharge='1')) then                 -- precharge
                        RAS_N <= '0';
                        CAS_N <= '1';
                        WE_N  <= '0';
                elsif (do_load_mode='1') then                 -- Mode Write: S=00, RAS=0, CAS=0, WE=0
                        RAS_N <= '0';
                        CAS_N <= '0';
                        WE_N  <= '0';
                elsif (do_reada = '1' or do_writea = '1') then  -- Activate: S=01 or 10, RAS=0, CAS=1, WE=1
                        RAS_N <= '0';
                        CAS_N <= '1';
                        WE_N  <= '1';
                elsif (do_rw = '1') then                      -- Read/Write:	S=01 or 10, RAS=1, CAS=0, WE=0 or 1
                        RAS_N <= '1';
                        CAS_N <= '0';
                        WE_N  <= rw_flag;
                else
                        RAS_N <= '1';
                        CAS_N <= '1';
                        WE_N  <= '1';
                end	if;
		end if;
	end process;





end RTL;