Implement ALU

fpga/src/alu.vhd

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+-- alu.vhd
+-- Created on: Di 26. Sep 10:07:59 CEST 2023
+-- Author(s): Yannick Reiß
+-- Content: Decode instructions and control brainfuck logic
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+-- Entity alu: alu crtl
+entity alu is
+    port(
+        instruction	:	in	std_logic_vector(2 downto 0);
+        old_cell	:	in	std_logic_vector(7 downto 0);
+        old_pointer :   in	std_logic_vector(15 downto 0);
+        extern_in	:   in	std_logic_vector(7 downto 0);
+
+        new_cell	:	out	std_logic_vector(7 downto 0);
+        new_pointer	:	out	std_logic_vector(15 downto 0);
+        enable_cell	:	out	std_logic;
+        enable_ptr	:	out	std_logic;
+        extern_out	:   out	std_logic_vector(7 downto 0)
+    );
+end alu;
+
+-- Architecture implementation of alu: implements table
+architecture implementation of alu is
+
+begin
+    -- Process p_instruction
+    p_instruction : process (instruction) -- runs only, when instruction changed
+    begin
+        case instruction is
+            when "000" =>
+                enable_cell <= '0';
+                enable_ptr  <= '1';
+                new_pointer <= std_logic_vector(unsigned(old_pointer) + 1);
+            when "001" =>
+                enable_cell <= '0';
+                enable_ptr  <= '1';
+                new_pointer <= std_logic_vector(unsigned(old_pointer) - 1);
+            when "010" =>
+                enable_cell <= '1';
+                enable_ptr  <= '0';
+                new_cell    <= std_logic_vector(unsigned(old_cell) + 1);
+            when "011" =>
+                enable_cell <= '1';
+                enable_ptr  <= '0';
+                new_cell    <= std_logic_vector(unsigned(old_cell) - 1);
+            when "100" =>
+                enable_cell <= '1';
+                enable_ptr  <= '0';
+                new_cell    <= extern_in;
+            when "101" =>
+                enable_cell <= '0';
+                enable_ptr  <= '0';
+                extern_out  <= old_cell;
+            when others =>
+                enable_cell <= '0';
+                enable_ptr  <= '0';
+        end case;
+    end process;
+
+end implementation;