Implement and connect branch

src/Decoder.vhd

@@ -9,11 +9,12 @@ use IEEE.numeric_std.all;
 -- Entity decode: Decoder currently supporting read operations
 entity Decoder is
   port(
-    Instruction : in  std_logic_vector(15 downto 0);  -- Instruction from instruction memory
-    AluOpcd     : out std_logic_vector(3 downto 0);  -- alu opcode
-    RegOp1      : out std_logic_vector(3 downto 0);  -- Rj: first register to read
-    RegOp2      : out std_logic_vector(3 downto 0);  -- Rk: second register to read
-    RegWrite    : out std_logic_vector(3 downto 0)  -- Ri: the register to write to
+    Instruction  : in  std_logic_vector(15 downto 0);  -- Instruction from instruction memory
+    AluOpcd      : out std_logic_vector(3 downto 0);  -- alu opcode
+    RegOp1       : out std_logic_vector(3 downto 0);  -- Rj: first register to read
+    RegOp2       : out std_logic_vector(3 downto 0);  -- Rk: second register to read
+    RegWrite     : out std_logic_vector(3 downto 0);  -- Ri: the register to write to
+    BranchEnable : out std_logic
     );
 end Decoder;
 
@@ -34,9 +35,16 @@ begin
     case Instruction(3 downto 0) is
       when "0000" | "0010" | "0011" | "0100" | "0101" | "0110" | "0111" | "1000" | "1010" => AluOpcd <= Instruction(3 downto 0);  -- R-Types
       when "0001" | "1001"                                                                => AluOpcd <= Instruction(7 downto 4);  -- S-Types
-      when "1110"                                                                         => AluOpcd <= Instruction(7 downto 4);  -- B-Types (to be debated)
+      when "1110"                                                                         => AluOpcd <= Instruction(15 downto 12);  -- B-Types (to be debated)
       when others                                                                         => AluOpcd <= "1111";  -- if unsure, do nothing
     end case;
+
+    -- BranchEnable
+    case Instruction(3 downto 0) is
+      when "0001" | "1001" | "0100" | "1100" | "0101" | "1101" =>
+        BranchEnable <= '1';
+      when others => BranchEnable <= '0';
+    end case;
   end process Decode;
 
 end Implementation;

src/branch.vhd

@@ -0,0 +1,27 @@
+-- branch.vhd
+-- Date:   Thu Feb  1 06:03:29 2024
+-- Author:    Yannick Reiß
+-- E-Mail:    schnick@nickr.eu
+library IEEE;
+use IEEE.std_logic_1164.all;
+use IEEE.numeric_std.all;
+
+entity Branch is
+  port (
+    BranchEnable : in  std_logic;
+    AluResult    : in  std_logic_vector(15 downto 0);
+    PC           : in  std_logic_vector(15 downto 0);
+    PMNext       : in  std_logic_vector(15 downto 0);
+    JumpSuggest  : out std_logic;
+    PCCalc       : out std_logic_vector(15 downto 0)
+    );
+end Branch;
+
+architecture Implementation of Branch is
+
+begin
+
+  PCCalc      <= std_logic_vector(signed(PC) + signed(PMNext));
+  JumpSuggest <= BranchEnable and AluResult(0);
+
+end Implementation;

src/cpu16.vhd

@@ -47,6 +47,8 @@ architecture Implementation of Cpu16 is
   signal I2CClient           : std_logic_vector(15 downto 0) := (others => '0');
   signal I2CClientOut        : std_logic_vector(15 downto 0) := (others => '0');
   signal I2CServer           : std_logic_vector(15 downto 0) := (others => '0');
+  signal PcAddrCalc          : std_logic_vector(15 downto 0) := (others => '0');
+  signal BranchEnable        : std_logic                     := '0';
 begin
 
   -- Include Entities
@@ -96,11 +98,12 @@ begin
 
   Decoder : entity work.Decoder(Implementation)
     port map(
-      Instruction => RawInstruction,
-      AluOpcd     => AluOpcode,
-      RegOp1      => RegisterRegister1,
-      RegOp2      => RegisterRegister2,
-      RegWrite    => RegisterRegisterW
+      Instruction  => RawInstruction,
+      AluOpcd      => AluOpcode,
+      RegOp1       => RegisterRegister1,
+      RegOp2       => RegisterRegister2,
+      RegWrite     => RegisterRegisterW,
+      BranchEnable => BranchEnable
       );
 
   ImmUseless : entity work.Immediate(Implementation)
@@ -113,7 +116,7 @@ begin
     port map(
       Clk      => Clk,
       PcEnable => PcEnable,
-      AddrCalc => AluResult,
+      AddrCalc => PcAddrCalc,
       Jump     => Jump,
       Addr     => InstructionCounter
       );
@@ -130,6 +133,16 @@ begin
       ClientW => I2CClientOut
       );
 
+  BranchEnabler : entity work.Branch(Implementation)
+    port map(
+      BranchEnable => BranchEnable,
+      AluResult    => AluResult,
+      PC           => InstructionCounter,
+      PMNext       => NextInstruction,
+      JumpSuggest  => Jump,
+      PCCalc       => PcAddrCalc
+      );
+
   AluSetInput : process(ImmediateValue, InstructionCounter, RegisterDataOut1,
                         RegisterDataOut2)
   begin
@@ -141,8 +154,6 @@ begin
                               AluIn2 <= ImmediateValue;
       when others => AluIn1 <= InstructionCounter;
                      AluIn2 <= RegisterDataOut2;
-
-
     end case;
   end process AluSetInput;