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[/] [wb_tk/] [trunk/] [wb_async_master.vhd] - Rev 7
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library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity wb_async_master is generic ( dat_width: positive := 16; adr_width: positive := 20; ab_rd_delay: positive := 1 ); port ( wb_clk_i: in std_logic; wb_rst_i: in std_logic := '0'; -- interface to wb slave devices wb_adr_o: out std_logic_vector (adr_width-1 downto 0); wb_sel_o: out std_logic_vector ((dat_width/8)-1 downto 0); wb_dat_i: in std_logic_vector (dat_width-1 downto 0); wb_dat_o: out std_logic_vector (dat_width-1 downto 0); wb_cyc_o: out std_logic; wb_ack_i: in std_logic; wb_err_i: in std_logic := '-'; wb_rty_i: in std_logic := '-'; wb_we_o: out std_logic; wb_stb_o: out std_logic; -- interface to the asyncronous master device ab_dat: inout std_logic_vector (dat_width-1 downto 0) := (others => 'Z'); ab_adr: in std_logic_vector (adr_width-1 downto 0) := (others => 'U'); ab_rd_n: in std_logic := '1'; ab_wr_n: in std_logic := '1'; ab_ce_n: in std_logic := '1'; ab_byteen_n: in std_logic_vector ((dat_width/8)-1 downto 0); ab_wait_n: out std_logic; -- wait-state request 'open-drain' output ab_waiths: out std_logic -- handshake-type totem-pole output ); end wb_async_master; architecture xilinx of wb_async_master is constant ab_wr_delay: positive := 2; -- delay lines for rd/wr edge detection signal rd_delay_rst: std_logic; signal rd_delay: std_logic_vector(ab_rd_delay downto 0); signal wr_delay: std_logic_vector(ab_wr_delay downto 0); -- one-cycle long pulses upon rd/wr edges signal ab_wr_pulse: std_logic; signal ab_rd_pulse: std_logic; -- one-cycle long pulse to latch address for writes signal ab_wr_latch_pulse: std_logic; -- WB data input register signal wb_dat_reg: std_logic_vector (dat_width-1 downto 0); -- internal copies of WB signals for feedback signal wb_cyc_l: std_logic; signal wb_we_l: std_logic; -- Comb. logic for active cycles signal ab_rd: std_logic; signal ab_wr: std_logic; signal ab_active: std_logic; -- internal copies of wait signals for feedback signal ab_wait_n_rst: std_logic; signal ab_wait_n_l: std_logic; signal ab_waiths_l: std_logic; signal ab_wait_n_l_delayed: std_logic; signal ab_waiths_l_delayed: std_logic; -- active when WB slave terminates the cycle (for any reason) signal wb_ack: std_logic; -- signals a scheduled or commencing posted write signal write_in_progress: std_logic; begin ab_rd <= (not ab_ce_n) and (not ab_rd_n) and ab_wr_n; ab_wr <= (not ab_ce_n) and (not ab_wr_n) and ab_rd_n; ab_active <= not ab_ce_n; wb_ack <= wb_cyc_l and (wb_ack_i or wb_err_i or wb_rty_i); write_in_progress_gen: process begin if (wb_rst_i = '1') then write_in_progress <= '0'; end if; wait until wb_clk_i'EVENT and wb_clk_i = '1'; if ab_wr = '0' and wr_delay(wr_delay'HIGH) = '1' then write_in_progress <= '1'; end if; if wb_ack = '1' then write_in_progress <= '0'; end if; end process; -- Registers addr/data lines. reg_bus_lines: process begin if (wb_rst_i = '1') then wb_adr_o <= (others => '-'); wb_sel_o <= (others => '-'); wb_dat_o <= (others => '-'); wb_dat_reg <= (others => '0'); end if; wait until wb_clk_i'EVENT and wb_clk_i = '1'; -- Store and sycnronize data and address lines if no (posted) write -- is in progress and there is an active asyncronous bus cycle. -- We store addresses for reads at the same time we sample the data so setup and hold -- times are the same. if (ab_wr = '1' or ab_rd_pulse = '1') and (write_in_progress = '0' or wb_ack = '1') then wb_adr_o <= ab_adr; for i in wb_sel_o'RANGE loop wb_sel_o(i) <= not ab_byteen_n(i); end loop; end if; if (ab_wr = '1') and (write_in_progress = '0' or wb_ack = '1') then wb_dat_o <= ab_dat; end if; -- en-register data input at the end of a read cycle if wb_ack = '1' then if wb_we_l = '0' then -- read cycle completed, store the result wb_dat_reg <= wb_dat_i; end if; end if; end process; -- Registers asycn bus control lines for sync edge detection. async_bus_wr_ctrl : process(wb_rst_i,wb_clk_i) begin if (wb_rst_i = '1') then wr_delay <= (others => '0'); -- end if; -- Post-layout simulation shows glitches on the output that violates setup times. -- Clock on the other edge to solve this issue -- elsif wb_clk_i'EVENT and wb_clk_i = '1' then elsif wb_clk_i'EVENT and wb_clk_i = '0' then -- wait until wb_clk_i'EVENT and wb_clk_i = '1'; -- wait until wb_clk_i'EVENT and wb_clk_i = '0'; -- delayed signals will be used in edge-detection for i in wr_delay'HIGH downto 1 loop wr_delay(i) <= wr_delay(i-1);-- and ab_rd; end loop; wr_delay(0) <= ab_wr; end if; end process; rd_delay_rst <= wb_rst_i or not ab_rd; async_bus_rd_ctrl : process(rd_delay_rst,wb_clk_i) begin if (rd_delay_rst = '1') then rd_delay <= (others => '0'); -- Post-layout simulation shows glitches on the output that violates setup times. -- Clock on the other edge to solve this issue -- elsif wb_clk_i'EVENT and wb_clk_i = '1' then elsif wb_clk_i'EVENT and wb_clk_i = '0' then -- a sync-reset shift-register to delay read signal for i in rd_delay'HIGH downto 1 loop rd_delay(i) <= rd_delay(i-1) and ab_rd; end loop; if (wb_cyc_l = '1') then rd_delay(0) <= rd_delay(0); else rd_delay(0) <= ab_rd and not write_in_progress; end if; end if; end process; -- will be one for one cycle at the proper end of the async cycle ab_wr_pulse <= wr_delay(wr_delay'HIGH) and not wr_delay(wr_delay'HIGH-1); ab_wr_latch_pulse <= not wr_delay(wr_delay'HIGH) and wr_delay(wr_delay'HIGH-1); ab_rd_pulse <= not rd_delay(rd_delay'HIGH) and rd_delay(rd_delay'HIGH-1); -- Generates WishBone control signals wb_ctrl_gen: process begin if (wb_rst_i = '1') then wb_stb_o <= '0'; wb_cyc_l <= '0'; wb_we_l <= '0'; end if; wait until wb_clk_i'EVENT and wb_clk_i = '1'; -- if wb_ack = '1' then if wb_ack = '1' and ab_wr_pulse = '0' and ab_rd_pulse = '0' then wb_stb_o <= '0'; wb_cyc_l <= '0'; wb_we_l <= '0'; end if; if ab_wr_pulse = '1' or ab_rd_pulse = '1' then wb_stb_o <= '1'; wb_cyc_l <= '1'; wb_we_l <= ab_wr_pulse; end if; end process; -- Generate asyncronous wait signal ab_wait_n_rst <= wb_rst_i or not ab_active; a_wait_n_gen: process(ab_wait_n_rst, wb_clk_i) begin if (ab_wait_n_rst = '1') then ab_wait_n_l <= '1'; elsif wb_clk_i'EVENT and wb_clk_i = '1' then -- At the beginning of a read cycle, move wait low if ab_wait_n_l = '1' and ab_rd = '1' and rd_delay(0) = '0' then ab_wait_n_l <= '0'; end if; -- At the beginning of any cycle, if the ss-master part is busy, wait if (ab_wait_n_l = '1' and (ab_rd = '1' or ab_wr = '1')) and (wb_cyc_l = '1') then ab_wait_n_l <= '0'; end if; -- At the end of an ss-master cycle, remove wait if wb_ack = '1' and ( (wb_we_l = '1' and ab_rd = '0') or -- no pending read wb_we_l = '0') -- was a read operation then ab_wait_n_l <= '1'; end if; end if; end process; -- Generate handshake-type wait signal a_waiths_gen: process(wb_rst_i,wb_clk_i) begin if (wb_rst_i = '1') then ab_waiths_l <= '0'; elsif wb_clk_i'EVENT and wb_clk_i = '1' then -- Write handling if wb_cyc_l = '0' and ab_wr = '1' then ab_waiths_l <= '1'; end if; if wb_ack = '1' and ab_waiths_l = '1' then ab_waiths_l <= '0'; end if; -- Read handling if wb_ack = '1' and ab_rd = '1' then ab_waiths_l <= '1'; end if; if wb_cyc_l = '0' and ab_rd = '0' and ab_wr = '0' and wr_delay(wr_delay'HIGH) = '0' then ab_waiths_l <= '0'; end if; end if; end process; -- connect local signals to external pins wb_cyc_o <= wb_cyc_l; wb_we_o <= wb_we_l; -- ab_wait_n <= '0' when ab_wait_n_l = '0' else '1'; ab_dat <= wb_dat_reg when ab_rd = '1' else (others => 'Z'); -- On post-layout simulation it turned out that the data is not stable upon -- the raising edge of these wait signals. So we delay the raising edge with one-half clock delay_wait: process(wb_clk_i) begin if wb_clk_i'EVENT and wb_clk_i = '0' then ab_wait_n_l_delayed <= ab_wait_n_l; ab_waiths_l_delayed <= ab_waiths_l; end if; end process; ab_wait_n <= ab_wait_n_l and ab_wait_n_l_delayed; ab_waiths <= ab_waiths_l and ab_waiths_l_delayed; -- ab_dat_gen: process(wb_clk_i,wb_rst_i) -- begin -- if (wb_rst_i = '1') then -- ab_dat <= (others => 'Z'); -- elsif wb_clk_i'EVENT and wb_clk_i = '1' then -- if (ab_rd = '1') then -- ab_dat <= wb_dat_reg; -- else -- ab_dat <= (others => 'Z'); -- end if; -- end if; -- end process; end xilinx;