Initial ALU Verilog

Currently using incorrect implementation for Multiply (* operator), to be fixed once Multiply method is decided
2024-12-22 21:45:49 +00:00 · 2020-05-29 14:16:02 +01:00 · 2020-05-29 14:16:02 +01:00 · 3f0c91b0ff
parent fedfcaaada
commit 3f0c91b0ff
1 changed files with 135 additions and 0 deletions
--- a/alu.v
+++ b/alu.v
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+module alu (enable, Rd, Rs1, Rs2, opcode, carryin, mulresult, carryout, mul1, mul2, Rout, jump);
+
+input enable; // active LOW, disables the ALU during load/store operations so that undefined behaviour does not occur
+input signed [15:0] Rd; // input destination register
+input signed [15:0] Rs1; // input source register 1
+input signed [15:0] Rs2; // input source register 2
+input [5:0] opcode; // opcode is fed in from instruction using wires outside ALU
+input carryin; // current status of carry flip-flop
+input signed [31:0] mulresult; // 32-bit result from multiplier
+
+output carryout; // resulting carry from operation, updated each cycle
+output reg signed [15:0] mul1; // first number to be multiplied
+output reg signed [15:0] mul2; // second number to be multiplied
+output signed [15:0] Rout; // value to be saved to destination register
+output jump; // tells decoder whether Jump condition is true
+
+// load and store are handled outside the ALU so those opcodes can be ignored. All other instructions have a consistent format.
+
+reg signed [16:0] alusum; // extra bit to hold carry from operations other than Multiply
+assign Rout = alusum [15:0];
+assign carryout = alusum [16];
+assign jump = (alusum[16] && ((opcode[5:2] == 4'b0000) | (opcode[5:2] == 4'b0001) | (opcode[5:2] == 4'b0010)));
+reg [15:0] mulextra;
+reg signed [31:0] mlaresult;
+
+//Jump Conditionals:
+wire JC1, JC2, JC3, JC4, JC5, JC6, JC7, JC8;
+assign JC1 = (Rs1 < Rs2);
+assign JC2 = (Rs1 > Rs2);
+assign JC3 = (Rs1 == Rs2);
+assign JC4 = (Rs1 == 0);
+assign JC5 = (Rs1 >= Rs2);
+assign JC6 = (Rs1 <= Rs2);
+assign JC7 = (Rs1 != Rs2);
+assign JC8 = (Rs1 < 0);
+
+always @(*)
+	begin
+		case (opcode)
+			6'b000000: alusum = {1'b1, Rd}; // JMP Unconditional Jump, first bit high to indicate jump and passes through Rd
+			
+			6'b000100: alusum = {JC1, Rd}; // JC1 Conditional Jump A < B
+			6'b000101: alusum = {JC2, Rd}; // JC2 Conditional Jump A > B
+			6'b000110: alusum = {JC3, Rd}; // JC3 Conditional Jump A = B
+			6'b000111: alusum = {JC4, Rd}; // JC4 Conditional Jump A = 0
+			
+			6'b001000: alusum = {JC5, Rd}; // JC5 Conditional Jump A >= B / A !< B
+			6'b001001: alusum = {JC6, Rd}; // JC6 Conditional Jump A <= B / A !> B
+			6'b001010: alusum = {JC7, Rd}; // JC7 Conditional Jump A != B
+			6'b001011: alusum = {JC8, Rd}; // JC8 Conditional Jump A < 0
+			
+			6'b001100: alusum = {1'b0, Rs1 & Rs2}; // AND Bitwise AND
+			6'b001101: alusum = {1'b0, Rs1 | Rs2}; // OR Bitwise OR
+			6'b001110: alusum = {1'b0, Rs1 ^ Rs2}; // XOR Bitwise XOR
+			6'b001111: alusum = {1'b0, ~Rs1}; // NOT Bitwise NOT
+			
+			6'b010000: alusum = {1'b0, ~Rs1 | ~Rs2}; // NND Bitwise NAND
+			6'b010001: alusum = {1'b0, ~Rs1 & ~Rs2}; // NOR Bitwise NOR
+			6'b010010: alusum = {1'b0, Rs1 ~^ Rs2}; // XNR Bitwise XNOR
+			6'b010011: alusum = {1'b0, Rs1}; // MOV Move (Rd = Rs1)
+			
+			6'b010100: alusum = {1'b0, Rs1} + {1'b0, Rs2}; // ADD Add (Rd = Rs1 + Rs2)
+			6'b010101: alusum = {1'b0, Rs1} + {1'b0, Rs2} + carryin; // ADC Add w/ Carry (Rd = Rs1 + Rs2 + C)
+			6'b010110: alusum = {1'b0, Rs1} + {17'b00000000000000001}; // ADO Add 1 (Rd = Rd + 1)
+			6'b010111: ;
+			
+			6'b011000: alusum = {1'b0, Rs1} - {1'b0, Rs2}; // SUB Subtract (Rd = Rs1 - Rs2)
+			6'b011001: alusum = {1'b0, Rs1} - {1'b0, Rs2} + carryin - {17'b00000000000000001}; // SBC Subtract w/ Carry (Rd = Rs1 - Rs2 + C - 1)
+			6'b011010: alusum = {1'b0, Rs1} - {17'b00000000000000001}; // SBO Subtract 1 (Rd = Rd - 1)
+			6'b011011: ;
+			
+			6'b011100: // MUL Multiply (Rd = Rs1 * Rs2)
+				begin
+//					mul1 = Rs1;
+//					mul2 = Rs2;
+					alusum[16] = 1'b0;
+					{mulextra, alusum[15:0]} = Rs1 * Rs2;
+				end
+			6'b011101: // MLA Multiply and Add  (Rd = Rs2 + (Rd * Rs1))
+				begin
+//					mul1 = Rs1;
+//					mul2 = Rs2;
+					alusum[16] = 1'b0;
+					{mulextra, alusum[15:0]} = (Rd * Rs1) + Rs2;
+				end
+			6'b011110: // MLS Multiply and Subtract (Rd = Rs2 - (Rd * Rs1)[15:0])
+				begin
+//					mul1 = Rs1;
+//					mul2 = Rs2;
+					alusum = {1'b0, Rs2 - (Rd * Rs1)};
+				end
+			6'b011111: alusum = mulextra; // MRT Retrieve Multiply MSBs (Rd = MSBs)
+			
+			6'b100000: alusum = {1'b0, Rs1 << Rs2}; // LSL Logical Shift Left (Rd = Rs1 shifted left by value of Rs2)
+			6'b100001: alusum = {1'b0, Rs1 >> Rs2}; // LSR Logical Shift Right (Rd = Rs1 shifted right by value of Rs2)
+			6'b100010: alusum = {Rs1[15], Rs1 >>> Rs2}; // ASR Arithmetic Shift Right (Rd = Rs1 shifted right by value of Rs2, maintaining sign bit)
+			6'b100011: ;
+			
+			6'b100100: alusum = {1'b0, (Rs1 >> Rs2[3:0]) | (Rs1 << (16 - Rs2[3:0]))}; // ROR Shift Right Loop (Rd = Rs1 shifted right by Rs2, but Rs1[0] -> Rs1[15])
+			6'b100101: alusum = ({Rs1, carryin} >> Rs2[3:0]) | ({Rs1, carryin} << (17 - (Rs2 % 17)));// RRC Shift Right Loop w/ Carry (Rd = Rs1 shifted right by Rs2, but Rs1[0] -> Carry & Carry -> Rs1[15])
+			6'b100110: ;
+			6'b100111: ;
+			
+			6'b111110: ; // NOP No Operation (Do Nothing for a cycle)
+			6'b111111: ; // STP Stop (Program Ends)
+			
+			default: ; // During Load & Store as well as undefined opcodes
+		endcase;
+	end
+
+/*	
+always @(*)
+	begin
+		case (opcode)
+			6'b011100:
+				begin
+					alusum = {1'b0, mulresult[15:0]};
+					mulextra = mulresult[31:16];
+				end
+			6'b011101:
+				begin
+					mlaresult = mulresult + {16'h0000, Rs2};
+					alusum = {1'b0, mlaresult[15:0]};
+					mulextra = mlaresult[31:16];
+				end
+			6'b011110:
+				begin
+					alusum = {1'b0, Rs2 - mulresult[15:0]};
+				end
+			default: ;
+		endcase
+	end
+*/
+
+endmodule