Implement scrolling_buffer and testbench for it

soc/peripheral/scrolling_buffer.vhd

@@ -0,0 +1,83 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity scrolling_buffer is
+    port(
+        clk : in std_logic;
+        rst : in std_logic;
+        buffer_clear : in std_logic;
+        buffer_write : in std_logic;
+        buffer_data : in std_logic_vector(4 downto 0);
+        next_char : in std_logic;
+        hex_char : out std_logic_vector(4 downto 0)
+    );
+end entity scrolling_buffer;
+
+architecture Behavioral of scrolling_buffer is
+
+    constant BUFFER_SIZE : integer := 16; 
+
+    type ring_buffer_type is array (0 to BUFFER_SIZE - 1) of std_logic_vector(4 downto 0);
+    signal ptr_write : integer range 0 to BUFFER_SIZE - 1;
+    signal ptr_read : integer range 0 to BUFFER_SIZE - 1;
+    signal ptr_last : integer range -1 to BUFFER_SIZE - 1;
+    
+    signal ring_buffer : ring_buffer_type;
+
+begin
+
+	process(clk)
+	begin
+		if clk'event and clk='1' then
+			if rst = '1' then
+                ptr_last <= -1;
+                ptr_write <= 0;
+                ring_buffer <= (others => (others => '0'));
+            else
+                if buffer_write = '1' then
+                    ring_buffer(ptr_write) <= buffer_data;
+                    
+                    if ptr_last /= BUFFER_SIZE - 1 then
+                        ptr_last <= ptr_write;
+                    end if;
+
+                    if ptr_write = BUFFER_SIZE - 1 then
+                        ptr_write <= 0;
+                    else
+                        ptr_write <= ptr_write + 1;
+                    end if;
+                elsif buffer_clear = '1' then
+                    ptr_last <= -1;
+                end if;
+            end if;
+		end if;
+	end process;
+
+    process(clk)
+	begin
+		if clk'event and clk='1' then
+			if rst = '1' then
+                ptr_read <= 0;
+                hex_char <= (others => '0');
+            else
+                hex_char <= (others => '0');
+            
+                if next_char = '1' then
+                    if ptr_last = -1 then -- Special case
+                        hex_char <= (others => '0');
+                    else
+                        hex_char <= ring_buffer(ptr_read);
+
+                        if ptr_read = ptr_last then
+                            ptr_read <= 0;
+                        else
+                            ptr_read <= ptr_read + 1;
+                        end if;
+                    end if;
+                end if;
+            end if;
+		end if;
+	end process;
+
+end Behavioral;

soc/testbench/scrolling_buffer_tb.vhd

@@ -0,0 +1,121 @@
+-- See the file "LICENSE" for the full license governing this code. --
+LIBRARY ieee;
+USE ieee.std_logic_1164.ALL;
+USE ieee.numeric_std.ALL;
+
+LIBRARY work;
+USE work.lt16soc_peripherals.ALL;
+
+ENTITY scrolling_buffer_tb IS
+END ENTITY;
+
+ARCHITECTURE sim OF scrolling_buffer_tb IS
+
+    constant CLK_PERIOD : time := 10 ns;
+
+    signal rst : std_logic;
+    signal clk : std_logic := '0';
+
+    signal buffer_clear : std_logic := '0';
+    signal buffer_write : std_logic := '0';
+    signal buffer_data : std_logic_vector(4 downto 0) := (others => '0');
+    signal next_char : std_logic := '0';
+    signal hex_char : std_logic_vector(4 downto 0);
+
+    component scrolling_buffer
+        port(
+            clk : in std_logic;
+            rst : in std_logic;
+            buffer_clear : in std_logic;
+            buffer_write : in std_logic;
+            buffer_data : in std_logic_vector(4 downto 0);
+            next_char : in std_logic;
+            hex_char : out std_logic_vector(4 downto 0)
+        );
+    end component;
+
+BEGIN
+
+	buf: scrolling_buffer
+        port map(
+			clk => clk,
+            rst => rst,
+            buffer_clear => buffer_clear,
+            buffer_write => buffer_write,
+            buffer_data => buffer_data,
+            next_char => next_char,
+            hex_char => hex_char
+    );
+
+    clk_gen: process
+	begin
+		clk	<= not clk;
+		wait for CLK_PERIOD/2;
+	end process clk_gen;
+
+	stimuli: process
+	begin
+        rst <= '1';
+        wait for CLK_PERIOD;
+
+        rst <= '0';
+        wait for CLK_PERIOD;
+
+        buffer_data <= "00001";
+        buffer_write <= '1';
+        
+        wait for CLK_PERIOD;
+        buffer_data <= "01011";
+        
+        wait for CLK_PERIOD;
+        buffer_write <= '0';
+        
+        wait for CLK_PERIOD;
+        buffer_data <= "01001";
+        buffer_write <= '1';
+        
+        wait for CLK_PERIOD;
+        buffer_data <= "00000";
+        buffer_write <= '0';
+        
+        wait for CLK_PERIOD;
+        next_char <= '1';
+        
+        wait for CLK_PERIOD;
+        assert hex_char = "00001" severity failure;
+        
+        wait for CLK_PERIOD;
+        assert hex_char = "01011" severity failure;
+        
+        wait for CLK_PERIOD;
+        assert hex_char = "01001" severity failure;
+        
+        wait for CLK_PERIOD;
+        next_char <= '0';
+        assert hex_char = "00001" severity failure; -- special case
+
+        wait for CLK_PERIOD * 3;
+        
+        -- Write buffer full
+        buffer_data <= "11111";
+        buffer_write <= '1';
+        
+        wait for CLK_PERIOD * 16;
+        buffer_data <= "00000";
+        buffer_write <= '0';
+        
+        wait for CLK_PERIOD;
+        next_char <= '1';
+
+		wait for CLK_PERIOD * 8;
+		buffer_clear <= '1';
+		
+		wait for CLK_PERIOD;
+		buffer_clear <= '0';
+		
+		wait for CLK_PERIOD * 8;
+
+		assert false report "Simulation terminated!" severity failure;
+	end process stimuli;
+
+END ARCHITECTURE;