starting files and example programs

1 files changed, 121 insertions, 0 deletions

diff --git a/PIC/tb_stack.vhd b/PIC/tb_stack.vhd
new file mode 100644
index 0000000..5b386e9
--- /dev/null
+++ b/PIC/tb_stack.vhd
@@ -0,0 +1,121 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity tb_stack is
+end entity tb_stack;
+
+architecture behavioural of tb_stack is
+  constant T_clk : time := 10 ns;
+  constant W     : positive := 13;
+
+  signal clk   : std_logic := '0';
+  signal reset : std_logic := '0';
+  signal push  : std_logic := '0';
+  signal pop   : std_logic := '0';
+  signal din   : std_logic_vector(W - 1 downto 0) := (others => '0');
+  signal dout  : std_logic_vector(W - 1 downto 0);
+
+  signal done : boolean := false;
+
+  procedure tick(signal clk_in : in std_logic) is
+  begin
+    wait until rising_edge(clk_in);
+    wait for 1 ns;
+  end procedure;
+
+begin
+
+  clk <= not clk after T_clk / 2 when not done else unaffected;
+
+  dut : entity work.stack(rtl)
+    generic map (DEPTH => 8, WIDTH => W)
+    port map (
+      clk   => clk,
+      reset => reset,
+      push  => push,
+      pop   => pop,
+      din   => din,
+      dout  => dout
+    );
+
+  stimulus : process is
+  begin
+
+    -- test 1: reset clears stack
+    report "test 1: reset";
+    reset <= '1';
+    wait for T_clk;
+    reset <= '0';
+    wait for 1 ns;
+    assert dout = std_logic_vector(to_unsigned(0, W))
+      report "reset: dout should be 0" severity error;
+
+    -- test 2: push one value and read it back
+    report "test 2: push/pop single value";
+    din  <= std_logic_vector(to_unsigned(16#42#, W));
+    push <= '1';
+    tick(clk);
+    push <= '0';
+    assert dout = std_logic_vector(to_unsigned(16#42#, W))
+      report "push: dout should be 0x42" severity error;
+    pop <= '1';
+    tick(clk);
+    pop <= '0';
+    assert dout = std_logic_vector(to_unsigned(0, W))
+      report "pop: dout should be 0 (empty)" severity error;
+
+    -- test 3: push multiple values, pop in LIFO order
+    report "test 3: LIFO order";
+    din  <= std_logic_vector(to_unsigned(16#100#, W));
+    push <= '1';
+    tick(clk);
+    din  <= std_logic_vector(to_unsigned(16#200#, W));
+    tick(clk);
+    din  <= std_logic_vector(to_unsigned(16#300#, W));
+    tick(clk);
+    push <= '0';
+    assert dout = std_logic_vector(to_unsigned(16#300#, W))
+      report "LIFO: top should be 0x300" severity error;
+    pop <= '1';
+    tick(clk);
+    assert dout = std_logic_vector(to_unsigned(16#200#, W))
+      report "LIFO: after 1 pop should be 0x200" severity error;
+    tick(clk);
+    assert dout = std_logic_vector(to_unsigned(16#100#, W))
+      report "LIFO: after 2 pops should be 0x100" severity error;
+    tick(clk);
+    pop <= '0';
+    assert dout = std_logic_vector(to_unsigned(0, W))
+      report "LIFO: stack empty, dout should be 0" severity error;
+
+    report "test 4: overflow wraparound";
+    push <= '1';
+    for i in 1 to 8 loop
+      din <= std_logic_vector(to_unsigned(i, W));
+      tick(clk);
+    end loop;
+    push <= '0';
+    -- after 8 pushes top wraps to 0, so stack looks empty
+    assert dout = std_logic_vector(to_unsigned(0, W))
+      report "overflow: top wrapped to 0, dout should be 0" severity error;
+
+    -- test 5: reset mid-operation clears pointer
+    report "test 5: reset mid-operation";
+    din  <= std_logic_vector(to_unsigned(16#1FF#, W));
+    push <= '1';
+    tick(clk);
+    push <= '0';
+    reset <= '1';
+    wait for T_clk;
+    reset <= '0';
+    wait for 1 ns;
+    assert dout = std_logic_vector(to_unsigned(0, W))
+      report "reset mid-op: dout should be 0" severity error;
+
+    report "All stack tests done" severity note;
+    done <= true;
+    wait;
+  end process stimulus;
+
+end architecture behavioural;