diff --git a/cores/curso/ch04/fifo_test.prj b/cores/curso/ch04/fifo_test.prj
new file mode 100644
index 0000000..4255fac
--- /dev/null
+++ b/cores/curso/ch04/fifo_test.prj
@@ -0,0 +1,2 @@
+vhdl work "list_ch04_21_fifo_test.vhd"
+vhdl work "list_ch04_20_fifo.vhd"
diff --git a/cores/curso/ch04/fifo_test.ut b/cores/curso/ch04/fifo_test.ut
new file mode 100644
index 0000000..a9facca
--- /dev/null
+++ b/cores/curso/ch04/fifo_test.ut
@@ -0,0 +1,30 @@
+-w
+-g Binary:no
+-g Compress
+-g CRC:Enable
+-g Reset_on_err:No
+-g ConfigRate:2
+-g ProgPin:PullUp
+-g TckPin:PullUp
+-g TdiPin:PullUp
+-g TdoPin:PullUp
+-g TmsPin:PullUp
+-g UnusedPin:PullDown
+-g UserID:0xFFFFFFFF
+-g ExtMasterCclk_en:No
+-g SPI_buswidth:1
+-g TIMER_CFG:0xFFFF
+-g multipin_wakeup:No
+-g StartUpClk:CClk
+-g DONE_cycle:4
+-g GTS_cycle:5
+-g GWE_cycle:6
+-g LCK_cycle:NoWait
+-g Security:None
+-g DonePipe:No
+-g DriveDone:No
+-g en_sw_gsr:No
+-g drive_awake:No
+-g sw_clk:Startupclk
+-g sw_gwe_cycle:5
+-g sw_gts_cycle:4
diff --git a/cores/curso/ch04/fifo_test.xst b/cores/curso/ch04/fifo_test.xst
new file mode 100644
index 0000000..5535fd4
--- /dev/null
+++ b/cores/curso/ch04/fifo_test.xst
@@ -0,0 +1,53 @@
+set -tmpdir "projnav.tmp"
+set -xsthdpdir "xst"
+run
+-ifn fifo_test.prj
+-infer_ramb8 No -loop_iteration_limit 32768
+-ofn fifo_test
+-ofmt NGC
+-p xc6slx9-2-tqg144
+-top fifo_test
+-opt_mode Speed
+-opt_level 2
+-power NO
+-uc "timings.xcf"
+-iuc NO
+-keep_hierarchy No
+-netlist_hierarchy As_Optimized
+-rtlview Yes
+-glob_opt AllClockNets
+-read_cores YES
+-write_timing_constraints YES
+-cross_clock_analysis NO
+-hierarchy_separator /
+-bus_delimiter <>
+-case Maintain
+-slice_utilization_ratio 100
+-bram_utilization_ratio 100
+-dsp_utilization_ratio 100
+-lc Auto
+-reduce_control_sets Auto
+-fsm_extract NO
+-fsm_style LUT
+-ram_extract Yes
+-ram_style Auto
+-rom_extract Yes
+-shreg_extract YES
+-rom_style Auto
+-auto_bram_packing NO
+-resource_sharing YES
+-async_to_sync YES
+-shreg_min_size 2
+-use_dsp48 Auto
+-iobuf YES
+-max_fanout 100000
+-bufg 16
+-register_duplication YES
+-register_balancing No
+-optimize_primitives NO
+-use_clock_enable Auto
+-use_sync_set Auto
+-use_sync_reset Auto
+-iob Auto
+-equivalent_register_removal YES
+-slice_utilization_ratio_maxmargin 5
diff --git a/cores/curso/ch04/list_ch04_17_18_watch.vhd b/cores/curso/ch04/list_ch04_17_18_watch.vhd
new file mode 100644
index 0000000..1185d2b
--- /dev/null
+++ b/cores/curso/ch04/list_ch04_17_18_watch.vhd
@@ -0,0 +1,134 @@
+--===================================
+-- Listing 4.17
+--===================================
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+entity stop_watch is
+   port(
+      clk: in std_logic;
+      go, clr: in std_logic;
+      d2, d1, d0: out std_logic_vector(3 downto 0)
+   );
+end stop_watch;
+
+architecture cascade_arch of stop_watch is
+   constant DVSR: integer:=5000000;
+   signal ms_reg, ms_next: unsigned(22 downto 0);
+   signal d2_reg, d1_reg, d0_reg: unsigned(3 downto 0);
+   signal d2_next, d1_next, d0_next: unsigned(3 downto 0);
+   signal d1_en, d2_en, d0_en: std_logic;
+   signal ms_tick, d0_tick, d1_tick: std_logic;
+begin
+   -- register
+   process(clk)
+   begin
+      if (clk'event and clk='1') then
+         ms_reg <= ms_next;
+         d2_reg <= d2_next;
+         d1_reg <= d1_next;
+         d0_reg <= d0_next;
+      end if;
+   end process;
+
+   -- next-state logic
+   -- 0.1 sec tick generator: mod-5000000
+   ms_next <=
+      (others=>'0') when clr='1' or
+                        (ms_reg=DVSR and go='1') else
+      ms_reg + 1 when go='1' else
+      ms_reg;
+   ms_tick <= '1' when ms_reg=DVSR else '0';
+   -- 0.1 sec counter
+   d0_en <= '1' when ms_tick='1' else '0';
+   d0_next <=
+      "0000" when (clr='1') or (d0_en='1' and d0_reg=9) else
+      d0_reg + 1 when d0_en='1' else
+      d0_reg;
+   d0_tick <= '1' when d0_reg=9 else '0';
+   -- 1 sec counter
+   d1_en <= '1' when ms_tick='1' and d0_tick='1' else '0';
+   d1_next <=
+      "0000" when (clr='1') or (d1_en='1' and d1_reg=9) else
+      d1_reg + 1 when d1_en='1' else
+      d1_reg;
+   d1_tick <= '1' when d1_reg=9 else '0';
+   -- 10 sec counter
+   d2_en <=
+      '1' when ms_tick='1' and d0_tick='1' and d1_tick='1' else
+      '0';
+   d2_next <=
+      "0000" when (clr='1') or (d2_en='1' and d2_reg=9) else
+      d2_reg + 1 when d2_en='1' else
+      d2_reg;
+
+   -- output logic
+   d0 <= std_logic_vector(d0_reg);
+   d1 <= std_logic_vector(d1_reg);
+   d2 <= std_logic_vector(d2_reg);
+end cascade_arch;
+
+
+--===================================
+-- Listing 4.18
+--===================================
+architecture if_arch of stop_watch is
+   constant DVSR: integer:=5000000;
+   signal ms_reg, ms_next: unsigned(22 downto 0);
+   signal d2_reg, d1_reg, d0_reg: unsigned(3 downto 0);
+   signal d2_next, d1_next, d0_next: unsigned(3 downto 0);
+   signal ms_tick: std_logic;
+begin
+   -- register
+   process(clk)
+   begin
+      if (clk'event and clk='1') then
+         ms_reg <= ms_next;
+         d2_reg <= d2_next;
+         d1_reg <= d1_next;
+         d0_reg <= d0_next;
+      end if;
+   end process;
+
+   -- next-state logic
+   -- 0.1 sec tick generator: mod-5000000
+   ms_next <=
+      (others=>'0') when clr='1' or
+                        (ms_reg=DVSR and go='1') else
+      ms_reg + 1 when go='1' else
+      ms_reg;
+   ms_tick <= '1' when ms_reg=DVSR else '0';
+   -- 0.1 sec counter
+   process(d0_reg,d1_reg,d2_reg,ms_tick,clr)
+   begin
+      -- defult
+      d0_next <= d0_reg;
+      d1_next <= d1_reg;
+      d2_next <= d2_reg;
+      if clr='1' then
+         d0_next <= "0000";
+         d1_next <= "0000";
+         d2_next <= "0000";
+      elsif ms_tick='1' then
+         if (d0_reg/=9) then
+            d0_next <= d0_reg + 1;
+         else       -- reach XX9
+            d0_next <= "0000";
+            if (d1_reg/=9) then
+               d1_next <= d1_reg + 1;
+            else    -- reach X99
+               d1_next <= "0000";
+               if (d2_reg/=9) then
+                  d2_next <= d2_reg + 1;
+               else -- reach 999
+                  d2_next <= "0000";
+               end if;
+            end if;
+         end if;
+      end if;
+   end process;
+   -- output logic
+   d0 <= std_logic_vector(d0_reg);
+   d1 <= std_logic_vector(d1_reg);
+   d2 <= std_logic_vector(d2_reg);
+end if_arch;
diff --git a/cores/curso/ch04/list_ch04_19_watch_test.vhd b/cores/curso/ch04/list_ch04_19_watch_test.vhd
new file mode 100644
index 0000000..6d93c7e
--- /dev/null
+++ b/cores/curso/ch04/list_ch04_19_watch_test.vhd
@@ -0,0 +1,34 @@
+--Listing 4.19
+library ieee;
+use ieee.std_logic_1164.all;
+entity stop_watch_test is
+   port(
+      clk: in std_logic;
+      bot: in std_logic_vector(4 downto 0);
+      sw: in std_logic_vector(7 downto 0);
+      led: out std_logic_vector(4 downto 0);
+      an: out std_logic_vector(3 downto 0);
+      sseg: out std_logic_vector(7 downto 0)
+   );
+end stop_watch_test;
+
+architecture arch of stop_watch_test is
+   signal d2, d1, d0: std_logic_vector(3 downto 0);
+   signal btn: std_logic_vector(1 downto 0);
+begin
+
+   led <= not bot;
+   btn <= not bot(1 downto 0);
+
+   disp_unit: entity work.disp_hex_mux
+      port map(
+         clk=>clk, reset=>'0',
+         hex3=>"0000", hex2=>d2, hex1=>d1, hex0=>d0,
+         point=>'1', colon=>'0',
+         an=>an, sseg=>sseg);
+
+   watch_unit: entity work.stop_watch(cascade_arch)
+      port map(
+         clk=>clk, go=>btn(1), clr=>btn(0),
+         d2 =>d2, d1=>d1, d0=>d0 );
+end arch;
diff --git a/cores/curso/ch04/list_ch04_20_fifo.vhd b/cores/curso/ch04/list_ch04_20_fifo.vhd
new file mode 100644
index 0000000..a347910
--- /dev/null
+++ b/cores/curso/ch04/list_ch04_20_fifo.vhd
@@ -0,0 +1,109 @@
+-- Listing 4.20
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+entity fifo is
+   generic(
+      B: natural:=8; -- number of bits
+      W: natural:=4 -- number of address bits
+   );
+   port(
+      clk, reset: in std_logic;
+      rd, wr: in std_logic;
+      w_data: in std_logic_vector (B-1 downto 0);
+      empty, full: out std_logic;
+      r_data: out std_logic_vector (B-1 downto 0)
+   );
+end fifo;
+
+architecture arch of fifo is
+   type reg_file_type is array (2**W-1 downto 0) of
+        std_logic_vector(B-1 downto 0);
+   signal array_reg: reg_file_type;
+   signal w_ptr_reg, w_ptr_next, w_ptr_succ:
+      std_logic_vector(W-1 downto 0);
+   signal r_ptr_reg, r_ptr_next, r_ptr_succ:
+      std_logic_vector(W-1 downto 0);
+   signal full_reg, empty_reg, full_next, empty_next:
+          std_logic;
+   signal wr_op: std_logic_vector(1 downto 0);
+   signal wr_en: std_logic;
+begin
+   --=================================================
+   -- register file
+   --=================================================
+   process(clk,reset)
+   begin
+     if (reset='1') then
+        array_reg <= (others=>(others=>'0'));
+     elsif (clk'event and clk='1') then
+        if wr_en='1' then
+           array_reg(to_integer(unsigned(w_ptr_reg)))
+                 <= w_data;
+        end if;
+     end if;
+   end process;
+   -- read port
+   r_data <= array_reg(to_integer(unsigned(r_ptr_reg)));
+   -- write enabled only when FIFO is not full
+   wr_en <= wr and (not full_reg);
+
+   --=================================================
+   -- fifo control logic
+   --=================================================
+   -- register for read and write pointers
+   process(clk,reset)
+   begin
+      if (reset='1') then
+         w_ptr_reg <= (others=>'0');
+         r_ptr_reg <= (others=>'0');
+         full_reg <= '0';
+         empty_reg <= '1';
+      elsif (clk'event and clk='1') then
+         w_ptr_reg <= w_ptr_next;
+         r_ptr_reg <= r_ptr_next;
+         full_reg <= full_next;
+         empty_reg <= empty_next;
+      end if;
+   end process;
+
+   -- successive pointer values
+   w_ptr_succ <= std_logic_vector(unsigned(w_ptr_reg)+1);
+   r_ptr_succ <= std_logic_vector(unsigned(r_ptr_reg)+1);
+
+   -- next-state logic for read and write pointers
+   wr_op <= wr & rd;
+   process(w_ptr_reg,w_ptr_succ,r_ptr_reg,r_ptr_succ,wr_op,
+           empty_reg,full_reg)
+   begin
+      w_ptr_next <= w_ptr_reg;
+      r_ptr_next <= r_ptr_reg;
+      full_next <= full_reg;
+      empty_next <= empty_reg;
+      case wr_op is
+         when "00" => -- no op
+         when "01" => -- read
+            if (empty_reg /= '1') then -- not empty
+               r_ptr_next <= r_ptr_succ;
+               full_next <= '0';
+               if (r_ptr_succ=w_ptr_reg) then
+                  empty_next <='1';
+               end if;
+            end if;
+         when "10" => -- write
+            if (full_reg /= '1') then -- not full
+               w_ptr_next <= w_ptr_succ;
+               empty_next <= '0';
+               if (w_ptr_succ=r_ptr_reg) then
+                  full_next <='1';
+               end if;
+            end if;
+         when others => -- write/read;
+            w_ptr_next <= w_ptr_succ;
+            r_ptr_next <= r_ptr_succ;
+      end case;
+   end process;
+   -- output
+   full <= full_reg;
+   empty <= empty_reg;
+end arch;
diff --git a/cores/curso/ch04/list_ch04_21_fifo_test.vhd b/cores/curso/ch04/list_ch04_21_fifo_test.vhd
new file mode 100644
index 0000000..e778a63
--- /dev/null
+++ b/cores/curso/ch04/list_ch04_21_fifo_test.vhd
@@ -0,0 +1,36 @@
+-- Listing 4.21
+library ieee;
+use ieee.std_logic_1164.all;
+entity fifo_test is
+   port(
+      clk: in std_logic;
+      bot: in std_logic_vector(4 downto 0);
+      sw: in std_logic_vector(7 downto 0);
+      led: out std_logic_vector(4 downto 0);
+      an: out std_logic_vector(3 downto 0);
+      sseg: out std_logic_vector(7 downto 0)
+   );
+end fifo_test;
+
+architecture arch of fifo_test is
+   signal btn, db_btn: std_logic_vector(2 downto 0);
+begin
+
+   sseg <= "11111111";
+   an <= "1111";
+   btn <= not bot(2 downto 0);
+
+   -- debounce circuit for btn(0)
+   btn_db_unit0: entity work.debounce(fsmd_arch)
+      port map(clk=>clk, reset=>btn(2), sw=>btn(0), db=>db_btn(0));
+   -- debounce circuit for btn(1)
+   btn_db_unit1: entity work.debounce(fsmd_arch)
+      port map(clk=>clk, reset=>btn(2), sw=>btn(1), db=>db_btn(1));
+   -- instantiate a 2^2-by-3 fifo)
+   fifo_unit: entity work.fifo(arch)
+      generic map(B=>3, W=>2)
+      port map(clk=>clk, reset=>btn(2),
+               rd=>db_btn(0), wr=>db_btn(1),
+               w_data=>sw(2 downto 0), r_data=>led(2 downto 0),
+               full=>led(4), empty=>led(3));
+end arch;
diff --git a/cores/curso/ch04/make.bat b/cores/curso/ch04/make.bat
index 6e3e2c4..1819d3c 100644
--- a/cores/curso/ch04/make.bat
+++ b/cores/curso/ch04/make.bat
@@ -1,10 +1,10 @@
 SET speed=2
 SET ruta_ucf=ch04
 SET ruta_bat=..\..\
-rem call :genbitstream disp_mux_test
+call :genbitstream disp_mux_test
 call :genbitstream hex_mux_test
-rem call :genbitstream shifter_test
-rem call :genbitstream fp_adder_test
+call :genbitstream stop_watch_test
+call :genbitstream fifo_test
 goto :eof
 
 :genbitstream
diff --git a/cores/curso/ch04/stop_watch_test.prj b/cores/curso/ch04/stop_watch_test.prj
new file mode 100644
index 0000000..dd31860
--- /dev/null
+++ b/cores/curso/ch04/stop_watch_test.prj
@@ -0,0 +1,2 @@
+vhdl work "list_ch04_19_watch_test.vhd"
+vhdl work "list_ch04_17_18_watch.vhd"
diff --git a/cores/curso/ch04/stop_watch_test.ut b/cores/curso/ch04/stop_watch_test.ut
new file mode 100644
index 0000000..a9facca
--- /dev/null
+++ b/cores/curso/ch04/stop_watch_test.ut
@@ -0,0 +1,30 @@
+-w
+-g Binary:no
+-g Compress
+-g CRC:Enable
+-g Reset_on_err:No
+-g ConfigRate:2
+-g ProgPin:PullUp
+-g TckPin:PullUp
+-g TdiPin:PullUp
+-g TdoPin:PullUp
+-g TmsPin:PullUp
+-g UnusedPin:PullDown
+-g UserID:0xFFFFFFFF
+-g ExtMasterCclk_en:No
+-g SPI_buswidth:1
+-g TIMER_CFG:0xFFFF
+-g multipin_wakeup:No
+-g StartUpClk:CClk
+-g DONE_cycle:4
+-g GTS_cycle:5
+-g GWE_cycle:6
+-g LCK_cycle:NoWait
+-g Security:None
+-g DonePipe:No
+-g DriveDone:No
+-g en_sw_gsr:No
+-g drive_awake:No
+-g sw_clk:Startupclk
+-g sw_gwe_cycle:5
+-g sw_gts_cycle:4
diff --git a/cores/curso/ch04/stop_watch_test.xst b/cores/curso/ch04/stop_watch_test.xst
new file mode 100644
index 0000000..f4c6f95
--- /dev/null
+++ b/cores/curso/ch04/stop_watch_test.xst
@@ -0,0 +1,53 @@
+set -tmpdir "projnav.tmp"
+set -xsthdpdir "xst"
+run
+-ifn stop_watch_test.prj
+-infer_ramb8 No -loop_iteration_limit 32768
+-ofn stop_watch_test
+-ofmt NGC
+-p xc6slx9-2-tqg144
+-top stop_watch_test
+-opt_mode Speed
+-opt_level 2
+-power NO
+-uc "timings.xcf"
+-iuc NO
+-keep_hierarchy No
+-netlist_hierarchy As_Optimized
+-rtlview Yes
+-glob_opt AllClockNets
+-read_cores YES
+-write_timing_constraints YES
+-cross_clock_analysis NO
+-hierarchy_separator /
+-bus_delimiter <>
+-case Maintain
+-slice_utilization_ratio 100
+-bram_utilization_ratio 100
+-dsp_utilization_ratio 100
+-lc Auto
+-reduce_control_sets Auto
+-fsm_extract NO
+-fsm_style LUT
+-ram_extract Yes
+-ram_style Auto
+-rom_extract Yes
+-shreg_extract YES
+-rom_style Auto
+-auto_bram_packing NO
+-resource_sharing YES
+-async_to_sync YES
+-shreg_min_size 2
+-use_dsp48 Auto
+-iobuf YES
+-max_fanout 100000
+-bufg 16
+-register_duplication YES
+-register_balancing No
+-optimize_primitives NO
+-use_clock_enable Auto
+-use_sync_set Auto
+-use_sync_reset Auto
+-iob Auto
+-equivalent_register_removal YES
+-slice_utilization_ratio_maxmargin 5