From 6bceee5e68e4f55949dcfbd1ebf5a138c50a9e07 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Tue, 5 Jun 2018 00:06:45 -0700
Subject: [PATCH] Initial commit. Working CPU!

---
 alu.sv      | 26 ++++++++++++++++
 cpu.sv      | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 memory.sv   | 15 +++++++++
 mux2.sv     |  6 ++++
 mux4.sv     | 24 +++++++++++++++
 register.sv | 18 +++++++++++
 6 files changed, 178 insertions(+)
 create mode 100644 alu.sv
 create mode 100644 cpu.sv
 create mode 100755 memory.sv
 create mode 100755 mux2.sv
 create mode 100755 mux4.sv
 create mode 100755 register.sv

diff --git a/alu.sv b/alu.sv
new file mode 100644
index 0000000..7993963
--- /dev/null
+++ b/alu.sv
@@ -0,0 +1,26 @@
+module alu #(width=32)
+			 (input logic [width-1:0] left, right,
+			  input logic [2:0] op,
+			  output logic [width-1:0] out);
+	logic [width-1:0] selected_right, not_right;
+	assign not_right = ~right;
+	mux2 #(width) right_mux(
+		.left(right),
+		.right(not_right),
+		.select(op[2]),
+		.out(selected_right));
+		
+	logic [width-1:0] op_and, op_or, op_sum, op_slt;
+	assign op_and = left & selected_right;
+	assign op_or = left | selected_right;
+	assign op_sum = left + selected_right + op[2];
+	assign op_slt = op_sum[width-1];
+	
+	mux4 output_mux(
+		.first(op_and),
+		.second(op_or),
+		.third(op_sum),
+		.fourth(op_slt),
+		.select(op[1:0]),
+		.out(out));
+endmodule
\ No newline at end of file
diff --git a/cpu.sv b/cpu.sv
new file mode 100644
index 0000000..826ab97
--- /dev/null
+++ b/cpu.sv
@@ -0,0 +1,89 @@
+module cpu 	(input logic clk, reset,
+			 input logic prog,
+			 input logic[31:0] pinst,
+			 input logic[7:0] paddr,
+			 output logic [31:0] disp);
+	logic [7:0] pc;
+	logic [7:0] pc_next, pc_compute;
+	logic [31:0] inst;
+	logic [5:0] op;
+	logic [2:0] rd, rs, rt;
+	logic [31:0] rd_val, rs_val, rt_val;
+	logic [15:0] const_val;
+	logic [31:0] const_extend;
+	logic [31:0] cpu_disp;
+	logic [31:0] reg_alu_out, const_alu_out;
+	logic should_jump, should_write, use_const;
+	
+	assign op = inst[31:26];
+	assign rd = inst[25:23];
+	assign rs = inst[22:20];
+	assign rt = inst[19:17];
+	assign const_val = inst[15:0];
+	
+	assign should_write = inst[31];
+	assign use_const = inst[30];
+	assign should_jump = inst[29];
+	
+	assign const_extend = const_val;
+	
+	registers #(32) regs(
+		.raddr1(rs),
+		.raddr2(rt),
+		.waddr(rd),
+		.in(rd_val),
+		.wen(should_write),
+		.clk(clk),
+		.reset(reset),
+		.out1(rs_val),
+		.out2(rt_val));
+	
+	memory #(32) insts(
+		.raddr(pc),
+		.waddr(paddr),
+		.wen(prog),
+		.in(pinst),
+		.clk(clk),
+		.out(inst),
+		.reset(reset));
+		
+	alu #(32) reg_alu(
+		.left(rs_val),
+		.right(rt_val),
+		.op(inst[28:26]),
+		.out(reg_alu_out));
+		
+	alu #(32) const_alu(
+		.left(rs_val),
+		.right(const_extend),
+		.op(inst[28:26]),
+		.out(const_alu_out));
+		
+	mux2 #(32) out_mux(
+		.left(reg_alu_out),
+		.right(const_alu_out),
+		.select(use_const),
+		.out(rd_val));
+		
+	assign pc_compute = rt_val + const_val;
+
+	mux2 #(8) pc_mux(
+		.left(pc + 1),
+		.right(pc_compute),
+		.select(should_jump & (inst[28] | (inst[26] ^ (rs_val == 0)))),
+		.out(pc_next));
+	
+	always_ff@(posedge clk) 
+		if(reset) begin
+			pc <= 0;
+			cpu_disp <= 0;
+		end else if(!prog) begin
+			case(op)
+				6'b0000000: cpu_disp <= rs_val;
+			endcase
+			pc <= pc_next;
+		end
+	
+	assign disp = cpu_disp;
+	
+endmodule
\ No newline at end of file
diff --git a/memory.sv b/memory.sv
new file mode 100755
index 0000000..2f18366
--- /dev/null
+++ b/memory.sv
@@ -0,0 +1,15 @@
+module memory #(width=32)
+				(input logic [7:0] raddr, waddr,
+				 input logic [width-1:0] in,
+				 input logic clk, wen, reset,
+				 output logic [width-1:0] out);
+	logic [width-1:0] data [0:255];
+	always_ff@(posedge clk)
+		if(reset) begin
+			data <= '{default: 0};
+		end else begin
+			if(wen) data[waddr] <= in;
+		end
+	
+	assign out = data[raddr];
+endmodule
\ No newline at end of file
diff --git a/mux2.sv b/mux2.sv
new file mode 100755
index 0000000..8cbfea5
--- /dev/null
+++ b/mux2.sv
@@ -0,0 +1,6 @@
+module mux2 #(width=32)
+			 (input logic [width-1:0] left, right,
+			  input logic select,
+			  output logic [width-1:0] out);
+	assign out = select ? right : left;
+endmodule
\ No newline at end of file
diff --git a/mux4.sv b/mux4.sv
new file mode 100755
index 0000000..98b3e92
--- /dev/null
+++ b/mux4.sv
@@ -0,0 +1,24 @@
+module mux4 #(width=32)
+			 (input logic [width-1:0] first, second, third, fourth,
+			  input logic [1:0] select,
+			  output logic [width-1:0] out);
+			  
+	logic [width-1:0] lower, upper;
+	
+	mux2 lower_mux(
+		.left(first),
+		.right(second),
+		.select(select[0]),
+		.out(lower));
+	mux2 upper_mux(
+		.left(third),
+		.right(fourth),
+		.select(select[0]),
+		.out(upper));
+		
+	mux2 final_mux(
+		.left(lower),
+		.right(upper),
+		.select(select[1]),
+		.out(out));
+endmodule
\ No newline at end of file
diff --git a/register.sv b/register.sv
new file mode 100755
index 0000000..d317d79
--- /dev/null
+++ b/register.sv
@@ -0,0 +1,18 @@
+module registers #(width=32)
+				   (input logic [2:0] raddr1, raddr2, waddr,
+				    input clk, wen, reset,
+					input logic [width-1:0] in,
+					output logic [width-1:0] out1, out2);
+	logic [width-1:0] data [0:7];
+				
+	always_ff@(posedge clk)
+		if (reset) begin
+			data <= '{default: 0};
+		end else begin
+			if(wen) data[waddr] <= in;
+		end
+
+	assign out1 = data[raddr1];
+	assign out2 = data[raddr2];
+	
+endmodule
\ No newline at end of file