From e4841407e608326a185ac74b984554078fc22204 Mon Sep 17 00:00:00 2001
From: Ibrahim <ibzmo28@gmail.com>
Date: Mon, 30 Nov 2020 14:07:33 +0000
Subject: [PATCH] ALU - start - questions need addressing

---
 rtl/mips_cpu_alu.v | 127 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 rtl/mips_cpu_alu.v

diff --git a/rtl/mips_cpu_alu.v b/rtl/mips_cpu_alu.v
new file mode 100644
index 0000000..e2a1844
--- /dev/null
+++ b/rtl/mips_cpu_alu.v
@@ -0,0 +1,127 @@
+/* Questions/Todos:
+
+-how to implement mult signed vs unsigned?
+-Need to clarify How many ALU ctrl flags there are
+-Need to go through & check special cases for each instruction
+-In the process of manually checking if every instruction has been accounted for in the actual enum
+-Right what your final set of different opeators each do (easy but somewhat tedious) :(
+*/
+
+
+
+
+module mips_cpu_alu(
+   input logic[31:0] A, B,//alu_in1, alu_in2 -The two ALU inputs
+
+   input logic [5:0] ALUFlags, //Output from ALU control - 6bits as there are 48 different instructions in our ISA that we need to implement
+
+    /*  The ALU Flags is 6 bits for now update when reduced */
+
+   output logic ALUZero, //Is the output of the ALU 0? - used to check result
+
+   output logic[31:0] ALUOut, // The ouput of the ALU 
+
+
+);
+
+ /* 
+ 
+ I have listed all of the instructions - reducing this set to figure out the size 
+ of ALUFlag/enum also need to go through the IS again and find special cases
+ (like over/underflow) for each instruction & to note them 
+ 
+ i.e. for the instruction  SLT (set on less than): 
+ ALUOut is '32'h000000001' if A < B
+ 
+  */
+
+// Instructions commented out have been accounted for 
+
+    /* Using an enum to define constants */
+    //typedef enum logic[5:0] {
+        //ADDIU = 6'd0, //Add immediate unsigned (no overflow)
+        //ADDU = 6'd1, 	//Add unsigned (no overflow)
+       //AND = 6'd2, 	//Bitwise and
+        //ANDI = 6'd3, 	//Bitwise and immediate
+        BEQ	 = 6'd4,    //Branch on equal
+        BGEZ = 6'd5, 	//Branch on greater than or equal to zero
+        BGEZAL = 6'd6, 	//Branch on non-negative (>=0) and link
+        BGTZ = 6'd7, 	//Branch on greater than zero
+        BLEZ = 6'd8, 	//Branch on less than or equal to zero
+        BLTZ = 6'd9, 	//Branch on less than zero
+        BLTZAL = 6'd10, //Branch on less than zero and link
+        BNE = 6'd11,    //Branch on not equal
+        //DIV = 6'd12, 	//Divide
+        //DIVU = 6'd13, 	//Divide unsigned
+        J = 6'd14, 	    //Jump
+        JALR = 6'd15, 	//Jump and link register
+        JAL = 6'd16, 	//Jump and link
+        JR = 6'd17, 	//Jump register
+        LB = 6'd18, 	//Load byte
+        LBU = 6'd19,   	//Load byte unsigned
+        LH = 6'd20, 	//Load half-word
+        LHU = 6'd21, 	//Load half-word unsigned
+        LUI = 6'd22, 	//Load upper immediate
+        LW = 6'd23, 	//Load word
+        LWL = 6'd24, 	//Load word left
+        LWR	= 6'd25,    //Load word right
+        MTHI = 6'd26, 	//Move to HI
+        MTLO = 6'd27, 	//Move to LO
+        //MULT = 6'd28, 	//Multiply
+        //MULTU = 6'd29, 	//Multiply unsigned
+        //OR = 6'd30, 	//Bitwise or
+        //ORI	= 6'd31,    //Bitwise or immediate
+        SB = 6'd32, 	//Store byte
+        SH = 6'd33, 	//Store half-word
+        SLL = 6'd34,    //Shift left logical
+        SLLV = 6'd35, 	//Shift left logical variable
+        SLT = 6'd36, 	//Set on less than (signed)
+        SLTI = 6'd37, 	//Set on less than immediate (signed)
+        SLTIU = 6'd38, 	//Set on less than immediate unsigned
+        SLTU = 6'd39, 	//Set on less than unsigned
+        SRA = 6'd40, 	//Shift right arithmetic
+        SRAV = 6'd41, 	//Shift right arithmetic
+        SRL = 6'd42, 	//Shift right logical
+        SRLV = 6'd43, 	//Shift right logical variable
+       //SUBU = 6'd44, 	//Subtract unsigned
+        SW = 6'd45, 	//Store word
+        XOR  = 6'd46,   //Bitwise exclusive or
+        XORI = 6'd47, 	//Bitwise exclusive or immediate
+    //} ALUFlags;
+
+/* This is how I believe our ctrl flags should be arranged */
+
+    typedef enum logic [/* ? */ : 0]{
+        ADD = 
+        SUB = 
+        MULT =
+        DIV = 
+        //logical
+        AND = 'd
+        OR = 'd
+        SLL = 'd
+
+    } ALUFlags;
+
+    always @(alu_in1, alu_in2, ALUFlags)
+    begin
+      case(ALUFlags)
+        ADD: begin
+            ALUOut = A & B; // is it = or <= ??
+        end
+
+        OR: begin
+            ALUOut = A | B;
+        end
+
+        SLL: begin
+            ALUOut = b >> shamt //Shamt is instruction read data [10:6]
+        end
+
+
+
+
+
+    end
+
+endmodule
\ No newline at end of file