Introducing the string sender

string_sender.gtkw

@@ -0,0 +1,27 @@
+[*]
+[*] GTKWave Analyzer v3.3.98 (w)1999-2019 BSI
+[*] Sat Jul 11 11:53:05 2020
+[*]
+[dumpfile] "/home/maximilian/vga_uart_grabber_vhdl/string_sender.vcd"
+[dumpfile_mtime] "Sat Jul 11 11:50:19 2020"
+[dumpfile_size] 410742
+[savefile] "/home/maximilian/vga_uart_grabber_vhdl/string_sender.gtkw"
+[timestart] 0
+[size] 1366 703
+[pos] -1 -1
+*-30.103638 200000000 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
+[treeopen] string_sender_tb.
+[sst_width] 212
+[signals_width] 299
+[sst_expanded] 1
+[sst_vpaned_height] 179
+@28
+string_sender_tb.tb_i_clk
+string_sender_tb.tb_i_reset_n
+string_sender_tb.tb_o_send
+@22
+string_sender_tb.tb_o_char[7:0]
+@29
+string_sender_tb.tb_i_sent
+[pattern_trace] 1
+[pattern_trace] 0

string_sender.vhdl

@@ -0,0 +1,77 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity string_sender is
+  port (
+        i_clk       :in std_logic;
+        i_send_clk  :in std_logic;
+        i_sent      :in std_logic;
+        i_reset_n   :in std_logic;
+        o_send      :out std_logic;
+        o_char      :out std_logic_vector(7 downto 0)
+       );
+end;
+
+architecture string_sender_rtl of string_sender is
+  type z_sender_t is (
+                      idle,
+                      wait_for_transmission,
+                      sending
+                    );
+  --Function to convert one char to std_logic_vector with 8 bit
+  function f_char_to_vector(
+    i_char : in character)
+    return std_logic_vector is
+    variable v_ret : std_logic_vector(7 downto 0);
+  begin
+    v_ret := std_logic_vector(
+              to_unsigned(natural(character'pos(i_char)),8)
+            );
+    return v_ret;
+  end function f_char_to_vector;
+
+begin
+  string_sender_main_proc: process(i_clk)
+    constant c_msg : string(1 to 13) := "Hello World!" & LF;
+    variable v_ind : integer range 0 to c_msg'length := 1;
+    variable v_old_clk : std_logic := '1';
+    variable z_sender : z_sender_t := idle;
+  begin
+    if rising_edge(i_clk) then
+      if i_reset_n = '0' then
+        v_ind := 1;
+        v_old_clk := i_send_clk;
+        z_sender := idle;
+        o_send <= '0';
+        o_char <= (others => '0');
+      else
+        case z_sender is
+          when idle =>
+            if (i_send_clk /= v_old_clk) then
+              v_old_clk := i_send_clk;
+              if (i_sent = '1') then
+                o_char <= f_char_to_vector(c_msg(v_ind));
+                o_send <= '1';
+                if v_ind = c_msg'length then
+                  v_ind := 1;
+                else
+                  v_ind := v_ind + 1;
+                end if;
+                z_sender := wait_for_transmission;
+              end if;
+            end if;
+          when wait_for_transmission =>
+            if i_sent = '0' then
+              o_send <= '0';
+              z_sender := sending;
+            end if;
+          when sending =>
+            if (i_sent = '1') then
+              z_sender := idle;
+            end if;
+        end case;
+      end if; -- reset
+    end if; -- clk
+  end process string_sender_main_proc;
+end;

string_sender_tb.vhdl

@@ -0,0 +1,100 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity string_sender_tb is
+end string_sender_tb;
+
+architecture string_sender_tb_rtl of string_sender_tb is
+  -- 10 MHz clock
+  constant c_CLK_PERIOD : time := 100 ns;
+  signal tb_i_clk       : std_logic := '0';
+  signal tb_i_send_clk  : std_logic := '0';
+  signal tb_i_sent      : std_logic := '1';
+  signal tb_i_reset_n   : std_logic := '1';
+  signal tb_o_send      : std_logic := '0';
+  signal tb_o_char      : std_logic_vector(7 downto 0) := (others => '0');
+  signal tb_done        : std_logic := '0';
+begin
+  string_send_0: entity work.string_sender(string_sender_rtl)
+  port map (
+            i_clk => tb_i_clk,
+            i_send_clk => tb_i_send_clk,
+            i_sent => tb_i_sent,
+            i_reset_n => tb_i_reset_n,
+            o_send => tb_o_send,
+            o_char => tb_o_char
+           );
+  -- Generate clock.
+  p_clock : process is
+  begin
+    if (tb_done = '0') then
+      tb_i_clk <= '0';
+      wait for c_CLK_PERIOD/2;
+      tb_i_clk <= '1';
+      wait for c_CLK_PERIOD/2;
+    elsif tb_done = '1' then
+      wait;
+    end if;
+  end process p_clock;
+  -- Generate send clock.
+  p_sclock : process is
+  begin
+    if (tb_done = '0') then
+      tb_i_send_clk <= '0';
+      wait for 10*(c_CLK_PERIOD/2);
+      tb_i_send_clk <= '1';
+      wait for 10*(c_CLK_PERIOD/2);
+    elsif tb_done = '1' then
+      wait;
+    end if;
+  end process p_sclock;
+  -- Process for stimuli.
+  p_stimuli : process is
+  begin
+    tb_i_reset_n <= '0';
+    wait for 2*c_CLK_PERIOD;
+    tb_i_reset_n <= '1';
+    wait for 1 ms;
+    tb_done <= '1';
+    assert false report "end of test" severity note;
+    wait;
+  end process p_stimuli;
+
+  p_ssp: process(tb_i_clk)
+    type z_ssp_t is (
+                    idle,
+                    busy,
+                    sending
+                  );
+    variable v_cnt : integer range 0 to 20 := 0;
+    variable z_ssp : z_ssp_t := idle;
+  begin
+    if rising_edge(tb_i_clk) then
+      case z_ssp is
+        when idle =>
+          if tb_o_send = '1' then
+            v_cnt := 0;
+            tb_i_sent <= '1';
+            z_ssp := busy;
+          end if;
+        when busy =>
+          if v_cnt = 10 then
+            v_cnt := 0;
+            tb_i_sent <= '0';
+            z_ssp := sending;
+          else
+            v_cnt := v_cnt + 1;
+          end if;
+        when sending =>
+          if v_cnt = 20 then
+            v_cnt := 0;
+            tb_i_sent <= '1';
+            z_ssp := idle;
+          else
+            v_cnt := v_cnt + 1;
+          end if;
+      end case;
+    end if;
+  end process p_ssp;
+end;